Deck 7: Physics

Question 1

Passage
Osteoporosis is a degenerative bone condition in which healthy bone degenerates into porous bone.  Because bone provides the structural integrity that allows the musculoskeletal system to bear weight, osteoporosis is associated with a higher risk of bone fracture.Researchers conducted an experiment designed to assess the strength and elasticity of osteoporotic bone relative to normal bone.  Osteoporotic and normal bone samples with identical physical dimensions were collected and placed within an pneumatic compression device, as shown in Figure 1.
Figure 1  Bone compression device loaded with a bone sampleThe force required to compress the bone samples longitudinally (lengthwise) by a given distance was measured, with the results shown in Figure 2.
Figure 2  Relationship between force and compression for normal and osteoporotic bonesResearchers observed that bone samples returned to their original dimensions for deformations not exceeding 1% of the original length L₀.  For each deformation, the associated strain ε is defined as the change in length of an object ΔL divided by the object's original length (Equation 1).
Equation 1Based on these observations, researchers concluded that both osteoporotic bone and normal bone behaved as an elastic material under a wide range of applied forces.
According to the data in Figure 2, what is the spring constant k for normal bone?

A)7.5 kN/mm
B)10 kN/mm
C)30 kN/mm
D)40 kN/mm

Answer 1

10 kN/mm

Question 2

Passage
In hemodynamics, blood flow through the cardiovascular system can be modeled as an electric circuit in which the blood serves as electricity, the blood vessels as resistive wires, and the heart as a battery (see Figure 1).
Figure 1  Cardiovascular circuit modelOhm's law states that the voltage drop ΔV across each element, the current I flowing through it, and its electrical resistance R are related by ΔV = IR.  In a blood vessel, pressure difference between one vessel and the next ΔP replaces ΔV, volumetric blood flow Q replaces I, and vascular resistance R replaces electrical resistance.  Therefore, Ohm's law for blood flow in a vessel isΔP = QREquation 1Vascular resistance is due to the blood's viscosity η and the dimensions of the vessel through which it flows.  Assuming blood vessels are cylinders, R can be approximated as
Equation 2where L is the length of the vessel, and r is its inner radius.  If Equation 2 is combined with Equation 1, the resulting equation is Poiseuille law.In a study of the circulatory system in rats, researchers measured the intravascular blood pressure of the mesenteric blood vessels.  The mesentery is the set of tissues that holds the intestines in place.  Blood flows in the following order:  aorta, superior mesenteric artery (SMA), arterial arcade, venous arcade, superior mesenteric vein (SMV).For the procedure, catheters with pressure transducers were inserted into each vessel via laparotomy.  Laparotomy is an invasive procedure that involves a surgical incision into the abdominal cavity.  Blood pressure measurements were taken simultaneously at the proximal end (beginning) of each blood vessel.
Figure 2  Mesenteric blood pressure profile of rats (Note: SMA = superior mesenteric artery; SMV = superior mesenteric vein.)
Which of the following can be used as units for η in Equation 2?

A)Pa⋅m2⋅
B)
C)Pa⋅s
D)

Answer 2

Pa⋅s

Question 3

Passage
Osteoporosis is a degenerative bone condition in which healthy bone degenerates into porous bone.  Because bone provides the structural integrity that allows the musculoskeletal system to bear weight, osteoporosis is associated with a higher risk of bone fracture.Researchers conducted an experiment designed to assess the strength and elasticity of osteoporotic bone relative to normal bone.  Osteoporotic and normal bone samples with identical physical dimensions were collected and placed within an pneumatic compression device, as shown in Figure 1.
Figure 1  Bone compression device loaded with a bone sampleThe force required to compress the bone samples longitudinally (lengthwise) by a given distance was measured, with the results shown in Figure 2.
Figure 2  Relationship between force and compression for normal and osteoporotic bonesResearchers observed that bone samples returned to their original dimensions for deformations not exceeding 1% of the original length L₀.  For each deformation, the associated strain ε is defined as the change in length of an object ΔL divided by the object's original length (Equation 1).
Equation 1Based on these observations, researchers concluded that both osteoporotic bone and normal bone behaved as an elastic material under a wide range of applied forces.
What is the pressure required to compress a normal bone sample by 1.5 mm?  (Note: The cross-sectional area of bone samples used in the experiment is 10 mm².)

A)1.10 kN/mm²
B)1.50 kN/mm²
C)110 kN/mm²
D)150 kN/mm²

Answer 3

1.50 kN/mm²

Question 4

Passage
The electric capacitance of biological tissues serves as the basis for numerous medical technologies.  For example, dielectric spectroscopy glucose reading (DSGR) is a noninvasive diagnostic technique that uses the electric capacitance of blood to estimate blood glucose levels.A DSGR device records the electric current that results from applying a voltage source to the skin and underlying blood vessels.  DSGR can be modeled by the circuit shown in Figure 1, in which V represents the applied potential, C_B represents the capacitance of the blood, and R_E, R_D, and R_B represent the electrical resistances of the epidermis, the dermis, and the blood, respectively.
Figure 1  DSGR circuit model including skin and superficial blood vesselThe capacitance of charged blood may be explained by red blood cell membranes acting as physical barriers that separate electrons introduced into the blood from positively charged ions in the red blood cell cytoplasm.  The dielectric constant k of red blood cell membranes varies with glucose concentration (Figure 2) because glucose uptake by red blood cells alters the activity of membrane-bound proteins that regulate the flow of ions into and out of the cell.
Figure 2  Blood dielectric constant vs blood glucose concentrationDSGR readings vary with blood glucose concentration because the time needed to fully charge the blood is related to total blood capacitance.  However, interpreting DSGR readings may be complicated by changes in biological variables other than blood capacitance.  For example, the resistivity of blood varies in accordance with osmolarity such that changes in diet or hydration status influence the current measured by DSGR devices.
Livshits, L. et al.  Dielectric response of biconcave erythrocyte membranes to D- and L-glucose.  J. Phys. D: Appl. Phys. 40 (2007), 15-19.
Assuming that the size and shape of red blood cells are uniform, by what factor would the quantity of red blood cells need to change to raise the capacitance of a blood sample to 250% of its original value?

A)2/5
B)(2/5)²
C)5/2
D)(5/2)²

Question 5

Passage
In hemodynamics, blood flow through the cardiovascular system can be modeled as an electric circuit in which the blood serves as electricity, the blood vessels as resistive wires, and the heart as a battery (see Figure 1).
Figure 1  Cardiovascular circuit modelOhm's law states that the voltage drop ΔV across each element, the current I flowing through it, and its electrical resistance R are related by ΔV = IR.  In a blood vessel, pressure difference between one vessel and the next ΔP replaces ΔV, volumetric blood flow Q replaces I, and vascular resistance R replaces electrical resistance.  Therefore, Ohm's law for blood flow in a vessel isΔP = QREquation 1Vascular resistance is due to the blood's viscosity η and the dimensions of the vessel through which it flows.  Assuming blood vessels are cylinders, R can be approximated as
Equation 2where L is the length of the vessel, and r is its inner radius.  If Equation 2 is combined with Equation 1, the resulting equation is Poiseuille law.In a study of the circulatory system in rats, researchers measured the intravascular blood pressure of the mesenteric blood vessels.  The mesentery is the set of tissues that holds the intestines in place.  Blood flows in the following order:  aorta, superior mesenteric artery (SMA), arterial arcade, venous arcade, superior mesenteric vein (SMV).For the procedure, catheters with pressure transducers were inserted into each vessel via laparotomy.  Laparotomy is an invasive procedure that involves a surgical incision into the abdominal cavity.  Blood pressure measurements were taken simultaneously at the proximal end (beginning) of each blood vessel.
Figure 2  Mesenteric blood pressure profile of rats (Note: SMA = superior mesenteric artery; SMV = superior mesenteric vein.)
Given the relationship between vascular resistance and blood pressure decay, which of the following blood vessel categories has the greatest total vascular resistance during systole?  (Note:  Vessel arcades are comprised of multiple individual blood vessels.)

A)Aorta
B)Arterial arcade
C)Venous arcade
D)Superior mesenteric artery

Question 6

Passage
During deep underwater dives, scuba divers must overcome the external ambient pressure in order to expand their chests to inhale.  To assist underwater breathing, air from scuba tanks is administered at high pressures to keep divers' lungs inflated.  Scuba tanks are often filled with a mixture of N₂ and O₂ gas.  Due to the increased pressure of the gases in the lungs, a greater amount of the gases are dissolved into the bloodstream during underwater dives.  At a body temperature of 37°C, the solubility of N₂ gas in blood is 6.0 × 10⁻³ mol/L⋅atm and the solubility of O₂ gas is 1.3 × 10⁻² mol/L⋅atm.If a diver ascends too quickly after an extended dive, there is an increased risk of vascular bubble formation.  Due to the decrease in ambient pressure, the excess gas dissolved in the blood may come out of solution as gas bubbles and cause a number of adverse effects.  This condition is known as decompression sickness, or "the bends."  To avoid this problem, scuba divers limit their rate of ascension to allow the excess gas dissolved in their blood to be safely removed through respiration.  Because gas bubbles are good reflectors of sound, these bubbles can be detected using Doppler ultrasonic flowmetry after the diver has surfaced.
Adapted from M. Spencer, Journal of Applied Physiology. ©1976 American Physiology Society.
Which of the following wave characteristics would be observed to increase if the bubbles are flowing toward the Doppler ultrasonic flow meter?

A)Frequency
B)Amplitude
C)Velocity
D)Wavelength

Question 7

Passage
In hemodynamics, blood flow through the cardiovascular system can be modeled as an electric circuit in which the blood serves as electricity, the blood vessels as resistive wires, and the heart as a battery (see Figure 1).
Figure 1  Cardiovascular circuit modelOhm's law states that the voltage drop ΔV across each element, the current I flowing through it, and its electrical resistance R are related by ΔV = IR.  In a blood vessel, pressure difference between one vessel and the next ΔP replaces ΔV, volumetric blood flow Q replaces I, and vascular resistance R replaces electrical resistance.  Therefore, Ohm's law for blood flow in a vessel isΔP = QREquation 1Vascular resistance is due to the blood's viscosity η and the dimensions of the vessel through which it flows.  Assuming blood vessels are cylinders, R can be approximated as
Equation 2where L is the length of the vessel, and r is its inner radius.  If Equation 2 is combined with Equation 1, the resulting equation is Poiseuille law.In a study of the circulatory system in rats, researchers measured the intravascular blood pressure of the mesenteric blood vessels.  The mesentery is the set of tissues that holds the intestines in place.  Blood flows in the following order:  aorta, superior mesenteric artery (SMA), arterial arcade, venous arcade, superior mesenteric vein (SMV).For the procedure, catheters with pressure transducers were inserted into each vessel via laparotomy.  Laparotomy is an invasive procedure that involves a surgical incision into the abdominal cavity.  Blood pressure measurements were taken simultaneously at the proximal end (beginning) of each blood vessel.
Figure 2  Mesenteric blood pressure profile of rats (Note: SMA = superior mesenteric artery; SMV = superior mesenteric vein.)
The blood pressures of an artery in the neck and in the leg of a person lying down are measured, and their difference calculated.  When the blood pressures are taken after the person stands up, their difference:

A)decreases because flow resistance is greater over horizontal distances.
B)remains the same because blood is modeled as an ideal fluid.
C)increases because viscous pressure acts in the direction of gravity.
D)increases due to the hydrostatic pressure between the two locations.

Question 8

Passage
Osteoporosis is a degenerative bone condition in which healthy bone degenerates into porous bone.  Because bone provides the structural integrity that allows the musculoskeletal system to bear weight, osteoporosis is associated with a higher risk of bone fracture.Researchers conducted an experiment designed to assess the strength and elasticity of osteoporotic bone relative to normal bone.  Osteoporotic and normal bone samples with identical physical dimensions were collected and placed within an pneumatic compression device, as shown in Figure 1.
Figure 1  Bone compression device loaded with a bone sampleThe force required to compress the bone samples longitudinally (lengthwise) by a given distance was measured, with the results shown in Figure 2.
Figure 2  Relationship between force and compression for normal and osteoporotic bonesResearchers observed that bone samples returned to their original dimensions for deformations not exceeding 1% of the original length L₀.  For each deformation, the associated strain ε is defined as the change in length of an object ΔL divided by the object's original length (Equation 1).
Equation 1Based on these observations, researchers concluded that both osteoporotic bone and normal bone behaved as an elastic material under a wide range of applied forces.
Researchers devised a different experiment to measure the torque required to fracture a long bone fixed in place at one end.  What information is required to calculate the torque?

A)Applied force, bone density, and angle of the applied force
B)Applied force, bone length, and angle of the applied force
C)Bone density, angle of the applied force, and bone length
D)Bone density, applied force, and bone length

Question 9

Passage
During deep underwater dives, scuba divers must overcome the external ambient pressure in order to expand their chests to inhale.  To assist underwater breathing, air from scuba tanks is administered at high pressures to keep divers' lungs inflated.  Scuba tanks are often filled with a mixture of N₂ and O₂ gas.  Due to the increased pressure of the gases in the lungs, a greater amount of the gases are dissolved into the bloodstream during underwater dives.  At a body temperature of 37°C, the solubility of N₂ gas in blood is 6.0 × 10⁻³ mol/L⋅atm and the solubility of O₂ gas is 1.3 × 10⁻² mol/L⋅atm.If a diver ascends too quickly after an extended dive, there is an increased risk of vascular bubble formation.  Due to the decrease in ambient pressure, the excess gas dissolved in the blood may come out of solution as gas bubbles and cause a number of adverse effects.  This condition is known as decompression sickness, or "the bends."  To avoid this problem, scuba divers limit their rate of ascension to allow the excess gas dissolved in their blood to be safely removed through respiration.  Because gas bubbles are good reflectors of sound, these bubbles can be detected using Doppler ultrasonic flowmetry after the diver has surfaced.
Adapted from M. Spencer, Journal of Applied Physiology. ©1976 American Physiology Society.
While underwater, divers designate their position with a buoy that floats at the surface above them.  Assuming the buoy is not pulled by the diver, what is the mass of a floating buoy that experiences a buoyancy force of 10 N and is 20% submerged?

A)1 kg
B)2 kg
C)5 kg
D)10 kg

Question 10

Passage
In hemodynamics, blood flow through the cardiovascular system can be modeled as an electric circuit in which the blood serves as electricity, the blood vessels as resistive wires, and the heart as a battery (see Figure 1).
Figure 1  Cardiovascular circuit modelOhm's law states that the voltage drop ΔV across each element, the current I flowing through it, and its electrical resistance R are related by ΔV = IR.  In a blood vessel, pressure difference between one vessel and the next ΔP replaces ΔV, volumetric blood flow Q replaces I, and vascular resistance R replaces electrical resistance.  Therefore, Ohm's law for blood flow in a vessel isΔP = QREquation 1Vascular resistance is due to the blood's viscosity η and the dimensions of the vessel through which it flows.  Assuming blood vessels are cylinders, R can be approximated as
Equation 2where L is the length of the vessel, and r is its inner radius.  If Equation 2 is combined with Equation 1, the resulting equation is Poiseuille law.In a study of the circulatory system in rats, researchers measured the intravascular blood pressure of the mesenteric blood vessels.  The mesentery is the set of tissues that holds the intestines in place.  Blood flows in the following order:  aorta, superior mesenteric artery (SMA), arterial arcade, venous arcade, superior mesenteric vein (SMV).For the procedure, catheters with pressure transducers were inserted into each vessel via laparotomy.  Laparotomy is an invasive procedure that involves a surgical incision into the abdominal cavity.  Blood pressure measurements were taken simultaneously at the proximal end (beginning) of each blood vessel.
Figure 2  Mesenteric blood pressure profile of rats (Note: SMA = superior mesenteric artery; SMV = superior mesenteric vein.)
Which change would result in the greatest decrease in the volumetric blood flow rate within a mesenteric vessel?

A)Decrease the viscosity of the blood by a factor of 4
B)Increase the length of the vessel by a factor of 9
C)Decrease the radius of the vessel by a factor of 2
D)Increase the pressure difference by a factor of 6

Question 11

Passage
Osteoporosis is a degenerative bone condition in which healthy bone degenerates into porous bone.  Because bone provides the structural integrity that allows the musculoskeletal system to bear weight, osteoporosis is associated with a higher risk of bone fracture.Researchers conducted an experiment designed to assess the strength and elasticity of osteoporotic bone relative to normal bone.  Osteoporotic and normal bone samples with identical physical dimensions were collected and placed within an pneumatic compression device, as shown in Figure 1.
Figure 1  Bone compression device loaded with a bone sampleThe force required to compress the bone samples longitudinally (lengthwise) by a given distance was measured, with the results shown in Figure 2.
Figure 2  Relationship between force and compression for normal and osteoporotic bonesResearchers observed that bone samples returned to their original dimensions for deformations not exceeding 1% of the original length L₀.  For each deformation, the associated strain ε is defined as the change in length of an object ΔL divided by the object's original length (Equation 1).
Equation 1Based on these observations, researchers concluded that both osteoporotic bone and normal bone behaved as an elastic material under a wide range of applied forces.
Which of the following expressions is equal to U_el, the elastic potential energy stored within a compressed bone?

A)
B)
C)
D)

Question 12

Passage
Osteoporosis is a degenerative bone condition in which healthy bone degenerates into porous bone.  Because bone provides the structural integrity that allows the musculoskeletal system to bear weight, osteoporosis is associated with a higher risk of bone fracture.Researchers conducted an experiment designed to assess the strength and elasticity of osteoporotic bone relative to normal bone.  Osteoporotic and normal bone samples with identical physical dimensions were collected and placed within an pneumatic compression device, as shown in Figure 1.
Figure 1  Bone compression device loaded with a bone sampleThe force required to compress the bone samples longitudinally (lengthwise) by a given distance was measured, with the results shown in Figure 2.
Figure 2  Relationship between force and compression for normal and osteoporotic bonesResearchers observed that bone samples returned to their original dimensions for deformations not exceeding 1% of the original length L₀.  For each deformation, the associated strain ε is defined as the change in length of an object ΔL divided by the object's original length (Equation 1).
Equation 1Based on these observations, researchers concluded that both osteoporotic bone and normal bone behaved as an elastic material under a wide range of applied forces.
If maintaining the maximal compression of an osteoporotic bone sample for 5 s requires 80 J of energy, what is the power expended by the compression machine?

A)8 J
B)16 W
C)40 J∙s
D)160 J∙s

Question 13

Passage
During deep underwater dives, scuba divers must overcome the external ambient pressure in order to expand their chests to inhale.  To assist underwater breathing, air from scuba tanks is administered at high pressures to keep divers' lungs inflated.  Scuba tanks are often filled with a mixture of N₂ and O₂ gas.  Due to the increased pressure of the gases in the lungs, a greater amount of the gases are dissolved into the bloodstream during underwater dives.  At a body temperature of 37°C, the solubility of N₂ gas in blood is 6.0 × 10⁻³ mol/L⋅atm and the solubility of O₂ gas is 1.3 × 10⁻² mol/L⋅atm.If a diver ascends too quickly after an extended dive, there is an increased risk of vascular bubble formation.  Due to the decrease in ambient pressure, the excess gas dissolved in the blood may come out of solution as gas bubbles and cause a number of adverse effects.  This condition is known as decompression sickness, or "the bends."  To avoid this problem, scuba divers limit their rate of ascension to allow the excess gas dissolved in their blood to be safely removed through respiration.  Because gas bubbles are good reflectors of sound, these bubbles can be detected using Doppler ultrasonic flowmetry after the diver has surfaced.
Adapted from M. Spencer, Journal of Applied Physiology. ©1976 American Physiology Society.
A diver is using a tank filled with 20% O₂ and 80% N₂ (by volume).  If the pressure in the lungs is 5 atm, what is the expected equilibrium concentration of N₂ dissolved in the diver's blood?  (Note:  Assume that the mixtures of the gases in the lungs and tank are equal.)

A)1.3 × 10⁻² mol/L
B)2.4 × 10⁻² mol/L
C)3.0 × 10⁻² mol/L
D)6.5 × 10⁻² mol/L

Question 14

Passage
The electric capacitance of biological tissues serves as the basis for numerous medical technologies.  For example, dielectric spectroscopy glucose reading (DSGR) is a noninvasive diagnostic technique that uses the electric capacitance of blood to estimate blood glucose levels.A DSGR device records the electric current that results from applying a voltage source to the skin and underlying blood vessels.  DSGR can be modeled by the circuit shown in Figure 1, in which V represents the applied potential, C_B represents the capacitance of the blood, and R_E, R_D, and R_B represent the electrical resistances of the epidermis, the dermis, and the blood, respectively.
Figure 1  DSGR circuit model including skin and superficial blood vesselThe capacitance of charged blood may be explained by red blood cell membranes acting as physical barriers that separate electrons introduced into the blood from positively charged ions in the red blood cell cytoplasm.  The dielectric constant k of red blood cell membranes varies with glucose concentration (Figure 2) because glucose uptake by red blood cells alters the activity of membrane-bound proteins that regulate the flow of ions into and out of the cell.
Figure 2  Blood dielectric constant vs blood glucose concentrationDSGR readings vary with blood glucose concentration because the time needed to fully charge the blood is related to total blood capacitance.  However, interpreting DSGR readings may be complicated by changes in biological variables other than blood capacitance.  For example, the resistivity of blood varies in accordance with osmolarity such that changes in diet or hydration status influence the current measured by DSGR devices.
Livshits, L. et al.  Dielectric response of biconcave erythrocyte membranes to D- and L-glucose.  J. Phys. D: Appl. Phys. 40 (2007), 15-19.
Suppose that a 5-mL blood sample with a glucose concentration of 10 mM has capacitance C.  How will C change if the concentration of blood glucose is reduced to 2.5 mM?

A)C will decrease by approximately 20%.
B)C will remain the same.
C)C will increase by approximately 20%.
D)C will increase by approximately 40%.

Question 15

Passage
Osteoporosis is a degenerative bone condition in which healthy bone degenerates into porous bone.  Because bone provides the structural integrity that allows the musculoskeletal system to bear weight, osteoporosis is associated with a higher risk of bone fracture.Researchers conducted an experiment designed to assess the strength and elasticity of osteoporotic bone relative to normal bone.  Osteoporotic and normal bone samples with identical physical dimensions were collected and placed within an pneumatic compression device, as shown in Figure 1.
Figure 1  Bone compression device loaded with a bone sampleThe force required to compress the bone samples longitudinally (lengthwise) by a given distance was measured, with the results shown in Figure 2.
Figure 2  Relationship between force and compression for normal and osteoporotic bonesResearchers observed that bone samples returned to their original dimensions for deformations not exceeding 1% of the original length L₀.  For each deformation, the associated strain ε is defined as the change in length of an object ΔL divided by the object's original length (Equation 1).
Equation 1Based on these observations, researchers concluded that both osteoporotic bone and normal bone behaved as an elastic material under a wide range of applied forces.
Compared to osteoporotic bone, the work required to compress normal bone by 2 mm is:

A)3/4 as great.
B)the same.
C)4/3 times greater.
D)8/3 times greater.

Question 16

Passage
During deep underwater dives, scuba divers must overcome the external ambient pressure in order to expand their chests to inhale.  To assist underwater breathing, air from scuba tanks is administered at high pressures to keep divers' lungs inflated.  Scuba tanks are often filled with a mixture of N₂ and O₂ gas.  Due to the increased pressure of the gases in the lungs, a greater amount of the gases are dissolved into the bloodstream during underwater dives.  At a body temperature of 37°C, the solubility of N₂ gas in blood is 6.0 × 10⁻³ mol/L⋅atm and the solubility of O₂ gas is 1.3 × 10⁻² mol/L⋅atm.If a diver ascends too quickly after an extended dive, there is an increased risk of vascular bubble formation.  Due to the decrease in ambient pressure, the excess gas dissolved in the blood may come out of solution as gas bubbles and cause a number of adverse effects.  This condition is known as decompression sickness, or "the bends."  To avoid this problem, scuba divers limit their rate of ascension to allow the excess gas dissolved in their blood to be safely removed through respiration.  Because gas bubbles are good reflectors of sound, these bubbles can be detected using Doppler ultrasonic flowmetry after the diver has surfaced.
Adapted from M. Spencer, Journal of Applied Physiology. ©1976 American Physiology Society.
What is the change in pressure when a diver descends from 10 m to 100 m below the water's surface?  (Note:  The density of water is 1,000 kg/m³.)

A)8.0 × 10⁵ N/m²
B)9.0 × 10⁵ N/m²
C)1.0 × 10⁶ N/m²
D)1.1 × 10⁶ N/m²

Question 17

Passage
During deep underwater dives, scuba divers must overcome the external ambient pressure in order to expand their chests to inhale.  To assist underwater breathing, air from scuba tanks is administered at high pressures to keep divers' lungs inflated.  Scuba tanks are often filled with a mixture of N₂ and O₂ gas.  Due to the increased pressure of the gases in the lungs, a greater amount of the gases are dissolved into the bloodstream during underwater dives.  At a body temperature of 37°C, the solubility of N₂ gas in blood is 6.0 × 10⁻³ mol/L⋅atm and the solubility of O₂ gas is 1.3 × 10⁻² mol/L⋅atm.If a diver ascends too quickly after an extended dive, there is an increased risk of vascular bubble formation.  Due to the decrease in ambient pressure, the excess gas dissolved in the blood may come out of solution as gas bubbles and cause a number of adverse effects.  This condition is known as decompression sickness, or "the bends."  To avoid this problem, scuba divers limit their rate of ascension to allow the excess gas dissolved in their blood to be safely removed through respiration.  Because gas bubbles are good reflectors of sound, these bubbles can be detected using Doppler ultrasonic flowmetry after the diver has surfaced.
Adapted from M. Spencer, Journal of Applied Physiology. ©1976 American Physiology Society.
An underwater diver is able to shine a laser onto the underwater portion of a distant boat.  However, the diver is unable to shine the laser onto the portion of the boat above the surface.  Which of the following best explains this phenomenon?

A)Diffraction
B)Dispersion
C)Reflection
D)Refraction

Question 18

Passage
In hemodynamics, blood flow through the cardiovascular system can be modeled as an electric circuit in which the blood serves as electricity, the blood vessels as resistive wires, and the heart as a battery (see Figure 1).
Figure 1  Cardiovascular circuit modelOhm's law states that the voltage drop ΔV across each element, the current I flowing through it, and its electrical resistance R are related by ΔV = IR.  In a blood vessel, pressure difference between one vessel and the next ΔP replaces ΔV, volumetric blood flow Q replaces I, and vascular resistance R replaces electrical resistance.  Therefore, Ohm's law for blood flow in a vessel isΔP = QREquation 1Vascular resistance is due to the blood's viscosity η and the dimensions of the vessel through which it flows.  Assuming blood vessels are cylinders, R can be approximated as
Equation 2where L is the length of the vessel, and r is its inner radius.  If Equation 2 is combined with Equation 1, the resulting equation is Poiseuille law.In a study of the circulatory system in rats, researchers measured the intravascular blood pressure of the mesenteric blood vessels.  The mesentery is the set of tissues that holds the intestines in place.  Blood flows in the following order:  aorta, superior mesenteric artery (SMA), arterial arcade, venous arcade, superior mesenteric vein (SMV).For the procedure, catheters with pressure transducers were inserted into each vessel via laparotomy.  Laparotomy is an invasive procedure that involves a surgical incision into the abdominal cavity.  Blood pressure measurements were taken simultaneously at the proximal end (beginning) of each blood vessel.
Figure 2  Mesenteric blood pressure profile of rats (Note: SMA = superior mesenteric artery; SMV = superior mesenteric vein.)
In the image shown, a simplified cardiovascular system is modeled as an electrical circuit.  Which of the following would occur if the blood flow to the brain is blocked?  (Assume that the blood pressure supplied by the heart remains unchanged.)

A)Total vascular flow resistance will increase
B)Pressure drop across the muscle will increase
C)Blood flow through the gut will always increase
D)Blood flow throughout the cardiovascular system will stop

Question 19

Passage
In hemodynamics, blood flow through the cardiovascular system can be modeled as an electric circuit in which the blood serves as electricity, the blood vessels as resistive wires, and the heart as a battery (see Figure 1).
Figure 1  Cardiovascular circuit modelOhm's law states that the voltage drop ΔV across each element, the current I flowing through it, and its electrical resistance R are related by ΔV = IR.  In a blood vessel, pressure difference between one vessel and the next ΔP replaces ΔV, volumetric blood flow Q replaces I, and vascular resistance R replaces electrical resistance.  Therefore, Ohm's law for blood flow in a vessel isΔP = QREquation 1Vascular resistance is due to the blood's viscosity η and the dimensions of the vessel through which it flows.  Assuming blood vessels are cylinders, R can be approximated as
Equation 2where L is the length of the vessel, and r is its inner radius.  If Equation 2 is combined with Equation 1, the resulting equation is Poiseuille law.In a study of the circulatory system in rats, researchers measured the intravascular blood pressure of the mesenteric blood vessels.  The mesentery is the set of tissues that holds the intestines in place.  Blood flows in the following order:  aorta, superior mesenteric artery (SMA), arterial arcade, venous arcade, superior mesenteric vein (SMV).For the procedure, catheters with pressure transducers were inserted into each vessel via laparotomy.  Laparotomy is an invasive procedure that involves a surgical incision into the abdominal cavity.  Blood pressure measurements were taken simultaneously at the proximal end (beginning) of each blood vessel.
Figure 2  Mesenteric blood pressure profile of rats (Note: SMA = superior mesenteric artery; SMV = superior mesenteric vein.)
Which of the following experimental groups would aid in determining if the procedure described in the passage has a confounding variable?

A)Group with laparotomy used without measuring blood pressure
B)Group with minimally invasive aortic catheterization to measure mesenteric blood pressure
C)Group fitted with noninvasive tail cuffs to measure systolic blood pressure
D)Group with laparotomy to measure renovascular blood pressure

Question 20

Passage
During deep underwater dives, scuba divers must overcome the external ambient pressure in order to expand their chests to inhale.  To assist underwater breathing, air from scuba tanks is administered at high pressures to keep divers' lungs inflated.  Scuba tanks are often filled with a mixture of N₂ and O₂ gas.  Due to the increased pressure of the gases in the lungs, a greater amount of the gases are dissolved into the bloodstream during underwater dives.  At a body temperature of 37°C, the solubility of N₂ gas in blood is 6.0 × 10⁻³ mol/L⋅atm and the solubility of O₂ gas is 1.3 × 10⁻² mol/L⋅atm.If a diver ascends too quickly after an extended dive, there is an increased risk of vascular bubble formation.  Due to the decrease in ambient pressure, the excess gas dissolved in the blood may come out of solution as gas bubbles and cause a number of adverse effects.  This condition is known as decompression sickness, or "the bends."  To avoid this problem, scuba divers limit their rate of ascension to allow the excess gas dissolved in their blood to be safely removed through respiration.  Because gas bubbles are good reflectors of sound, these bubbles can be detected using Doppler ultrasonic flowmetry after the diver has surfaced.
Adapted from M. Spencer, Journal of Applied Physiology. ©1976 American Physiology Society.
A 10-L scuba tank is initially filled with 2,800 g of N₂ gas.  At room temperature (25°C), what is the pressure in the tank?  (Note:  Use R = 0.0821 L⋅atm/mol⋅K.)

A)120 atm
B)240 atm
C)360 atm
D)480 atm

Question 21

Passage
For a person with perfect vision, light from an object is properly refracted by the eye lens to converge on a single point at the retina, forming a clear image of the object.  Vision defects result from eye shape abnormalities or errors in the refractive power of the eye lens.  Myopia (nearsightedness) occurs when light from a distant object is incorrectly focused in front of the retina.  Hyperopia (farsightedness) occurs when light rays from a nearby object are focused beyond the retina.Many optical techniques are available to measure the refractive error of an individual to determine the necessary correction.  Photorefraction is a photographic technique often used with young children because it does not require the individual to be still for a lengthy duration.  When the patient is looking at the camera, a flash photograph is taken of the eye to determine the amount of light that is reflected off the retina and captured by the camera lens.In healthy eyes, all the light from the flash that enters the eye is reflected off the retina and returns back to the camera's light source.  Because the camera lens does not receive this light, the pupil is completely dark in the resulting image.  A myopic eye cannot properly focus the light at the retina.  Due to the geometry of the eye and its lens, some of the light is reflected to the top portion of the camera lens.  The camera captures an image of a pupil with a crescent of light at the top.  In a hyperopic eye, the crescent appears at the bottom of the pupil.  Ray diagrams for photorefraction are shown in Figure 1.
Figure 1  Paths of light in photorefraction for different eyes:  (A) Healthy, (B) Myopic, and (C) Hyperopic.
HC. Howland, "Optics of photorefraction: orthogonal and isotropic methods." ©1983 Optical Society of America.
A patient's eye lens has a focal length of 2 cm.  When the patient wears a pair of prescription eyeglasses with an optical power of −4 D, the combined strength of the lenses is approximately:

A)42 D
B)46 D
C)50 D
D)54 D

Question 22

Passage
A traumatic brain injury (TBI) is a form of brain injury caused by an external physical force.  In addition to direct injury at the site of an impact, the rapid acceleration-deceleration of the head may cause the brain to move within the skull and result in injury to the part of the brain opposite the impact site.  This is known as a contrecoup injury.If an impact to the head also results in a skull fracture, the injury is classified as an open TBI.  If there is no skull fracture, the injury is classified as a closed TBI.  The type of TBI can be predicted from the collision duration and the average acceleration of the head.  The thresholds for open and closed TBI are shown in Figure 1.
Figure 1  Thresholds for open and closed TBIIn an experiment to study head collisions with projectiles, researchers equipped the head of a crash test dummy with sensors that measured acceleration on multiple axes.  The crash test dummy was stationary before its head was subjected to controlled collisions with incoming projectiles of varying mass and impact velocity.  The linear acceleration of the crash test dummy's head was recorded during and after the impact.  The results for a trial in which the impact lasted for 10 ms are shown in Figure 2.
Figure 2  The acceleration of the head during and after a 10-ms collision
In one experimental trial, the projectile was uniformly accelerated from rest to a distance of 2 m in 0.1 s.  What was the acceleration of the projectile?

A)20 m/s²
B)40 m/s²
C)200 m/s²
D)400 m/s²

Question 23

Passage
The electric capacitance of biological tissues serves as the basis for numerous medical technologies.  For example, dielectric spectroscopy glucose reading (DSGR) is a noninvasive diagnostic technique that uses the electric capacitance of blood to estimate blood glucose levels.A DSGR device records the electric current that results from applying a voltage source to the skin and underlying blood vessels.  DSGR can be modeled by the circuit shown in Figure 1, in which V represents the applied potential, C_B represents the capacitance of the blood, and R_E, R_D, and R_B represent the electrical resistances of the epidermis, the dermis, and the blood, respectively.
Figure 1  DSGR circuit model including skin and superficial blood vesselThe capacitance of charged blood may be explained by red blood cell membranes acting as physical barriers that separate electrons introduced into the blood from positively charged ions in the red blood cell cytoplasm.  The dielectric constant k of red blood cell membranes varies with glucose concentration (Figure 2) because glucose uptake by red blood cells alters the activity of membrane-bound proteins that regulate the flow of ions into and out of the cell.
Figure 2  Blood dielectric constant vs blood glucose concentrationDSGR readings vary with blood glucose concentration because the time needed to fully charge the blood is related to total blood capacitance.  However, interpreting DSGR readings may be complicated by changes in biological variables other than blood capacitance.  For example, the resistivity of blood varies in accordance with osmolarity such that changes in diet or hydration status influence the current measured by DSGR devices.
Livshits, L. et al.  Dielectric response of biconcave erythrocyte membranes to D- and L-glucose.  J. Phys. D: Appl. Phys. 40 (2007), 15-19.
Assume that the average radial artery has a cross-sectional area A of 0.2 cm² and a length L of 30 cm.  What is the total resistance R of the radial artery?  (Note: The resistivity of blood is 200 Ω-cm.)

A)3 × 10¹ Ω
B)3 × 10² Ω
C)3 × 10³ Ω
D)3 × 10⁴ Ω

Question 24

Passage
The humerus bone in the upper arm and the radius bone in the lower arm can be modeled as a lever with the elbow joint as the pivot point.  Movement about the elbow results from a combination of internal and external forces acting on these bones.  The primary internal force is generated from contractions of skeletal muscles; a 1-cm² cross-sectional area of skeletal muscle can generate a maximum of 7 × 10⁶ dynes of force (1 dyn = 1 g⋅cm/s²).  Friction between the humerus and the radius at the elbow is another internal force that can affect arm movements.  As people age, cartilage degeneration decreases the lubrication between bones, which increases the coefficients of static and kinetic friction.The contraction of the biceps, a skeletal muscle in the upper arm, exerts a pulling force on the radius in the lower arm.  If the torque generated by this muscle exceeds that of any opposing internal and external forces, the arm curls about the elbow.  This specific type of movement is known as a concentric muscle contraction.The following experiments were performed with a 30-year-old male subject.  Electrodes were placed around the subject's biceps and attached to an electromyograph, a device that measures the electrical activity of skeletal muscle contractions.  The estimated weight of the subject's lower arm is 45 N, and the subject's lower arm segments to the elbow are shown in Table 1.Table 1  Lower Arm Segment Lengths
 Experiment 1The subject kept his entire arm stationary and in a fixed position while holding balls of varying masses.  The upper arm was perpendicular to the ground, and the lower arm was parallel to the ground (Figure 1).
Figure 1  The fixed position of the arm during Experiment 1Experiment 2The subject kept his upper arm stationary and perpendicular to the ground while lifting and lowering balls of varying masses.
Adapted from N. Ozkaya, Fundamentals of Biomechanics. (C) 2016 Springer.
During Experiment 2, the subject lifts a ball with a mass m a vertical distance d₁ and then lowers the ball a greater vertical distance d₂.  What is the net work done by gravity on the ball?

A)W = 0 for all cases because gravity is a conservative force
B)W = mg(d₂ − d₁), because gravity does work to lift and lower the ball
C)W = mgd₂, because gravity does work only to lower the ball
D)W = mg(d₁ + d₂), because gravity does work only on the net vertical path

Question 25

Passage
The humerus bone in the upper arm and the radius bone in the lower arm can be modeled as a lever with the elbow joint as the pivot point.  Movement about the elbow results from a combination of internal and external forces acting on these bones.  The primary internal force is generated from contractions of skeletal muscles; a 1-cm² cross-sectional area of skeletal muscle can generate a maximum of 7 × 10⁶ dynes of force (1 dyn = 1 g⋅cm/s²).  Friction between the humerus and the radius at the elbow is another internal force that can affect arm movements.  As people age, cartilage degeneration decreases the lubrication between bones, which increases the coefficients of static and kinetic friction.The contraction of the biceps, a skeletal muscle in the upper arm, exerts a pulling force on the radius in the lower arm.  If the torque generated by this muscle exceeds that of any opposing internal and external forces, the arm curls about the elbow.  This specific type of movement is known as a concentric muscle contraction.The following experiments were performed with a 30-year-old male subject.  Electrodes were placed around the subject's biceps and attached to an electromyograph, a device that measures the electrical activity of skeletal muscle contractions.  The estimated weight of the subject's lower arm is 45 N, and the subject's lower arm segments to the elbow are shown in Table 1.Table 1  Lower Arm Segment Lengths
 Experiment 1The subject kept his entire arm stationary and in a fixed position while holding balls of varying masses.  The upper arm was perpendicular to the ground, and the lower arm was parallel to the ground (Figure 1).
Figure 1  The fixed position of the arm during Experiment 1Experiment 2The subject kept his upper arm stationary and perpendicular to the ground while lifting and lowering balls of varying masses.
Adapted from N. Ozkaya, Fundamentals of Biomechanics. (C) 2016 Springer.
Ignoring the weight of the arm, what is the mechanical advantage of the biceps when it is lifting a ball in Experiment 2?

A)0.07
B)0.10
C)10
D)15

Question 26

Passage
For a person with perfect vision, light from an object is properly refracted by the eye lens to converge on a single point at the retina, forming a clear image of the object.  Vision defects result from eye shape abnormalities or errors in the refractive power of the eye lens.  Myopia (nearsightedness) occurs when light from a distant object is incorrectly focused in front of the retina.  Hyperopia (farsightedness) occurs when light rays from a nearby object are focused beyond the retina.Many optical techniques are available to measure the refractive error of an individual to determine the necessary correction.  Photorefraction is a photographic technique often used with young children because it does not require the individual to be still for a lengthy duration.  When the patient is looking at the camera, a flash photograph is taken of the eye to determine the amount of light that is reflected off the retina and captured by the camera lens.In healthy eyes, all the light from the flash that enters the eye is reflected off the retina and returns back to the camera's light source.  Because the camera lens does not receive this light, the pupil is completely dark in the resulting image.  A myopic eye cannot properly focus the light at the retina.  Due to the geometry of the eye and its lens, some of the light is reflected to the top portion of the camera lens.  The camera captures an image of a pupil with a crescent of light at the top.  In a hyperopic eye, the crescent appears at the bottom of the pupil.  Ray diagrams for photorefraction are shown in Figure 1.
Figure 1  Paths of light in photorefraction for different eyes:  (A) Healthy, (B) Myopic, and (C) Hyperopic.
HC. Howland, "Optics of photorefraction: orthogonal and isotropic methods." ©1983 Optical Society of America.
Myopia can be corrected with a:

A)diverging lens, which creates real and inverted images.
B)diverging lens, which creates virtual and upright images.
C)converging lens, which creates real and inverted images.
D)converging lens, which creates virtual and upright images.

Question 27

Passage
A traumatic brain injury (TBI) is a form of brain injury caused by an external physical force.  In addition to direct injury at the site of an impact, the rapid acceleration-deceleration of the head may cause the brain to move within the skull and result in injury to the part of the brain opposite the impact site.  This is known as a contrecoup injury.If an impact to the head also results in a skull fracture, the injury is classified as an open TBI.  If there is no skull fracture, the injury is classified as a closed TBI.  The type of TBI can be predicted from the collision duration and the average acceleration of the head.  The thresholds for open and closed TBI are shown in Figure 1.
Figure 1  Thresholds for open and closed TBIIn an experiment to study head collisions with projectiles, researchers equipped the head of a crash test dummy with sensors that measured acceleration on multiple axes.  The crash test dummy was stationary before its head was subjected to controlled collisions with incoming projectiles of varying mass and impact velocity.  The linear acceleration of the crash test dummy's head was recorded during and after the impact.  The results for a trial in which the impact lasted for 10 ms are shown in Figure 2.
Figure 2  The acceleration of the head during and after a 10-ms collision
What additional information do the researchers need from the crash test dummy to estimate the power of the collision in the experiment shown in Figure 2?

A)Mass of the head
B)Time until the head stops moving
C)Tension of the neck during the collision
D)Velocity of the head at the end of the collision

Question 28

Passage
A traumatic brain injury (TBI) is a form of brain injury caused by an external physical force.  In addition to direct injury at the site of an impact, the rapid acceleration-deceleration of the head may cause the brain to move within the skull and result in injury to the part of the brain opposite the impact site.  This is known as a contrecoup injury.If an impact to the head also results in a skull fracture, the injury is classified as an open TBI.  If there is no skull fracture, the injury is classified as a closed TBI.  The type of TBI can be predicted from the collision duration and the average acceleration of the head.  The thresholds for open and closed TBI are shown in Figure 1.
Figure 1  Thresholds for open and closed TBIIn an experiment to study head collisions with projectiles, researchers equipped the head of a crash test dummy with sensors that measured acceleration on multiple axes.  The crash test dummy was stationary before its head was subjected to controlled collisions with incoming projectiles of varying mass and impact velocity.  The linear acceleration of the crash test dummy's head was recorded during and after the impact.  The results for a trial in which the impact lasted for 10 ms are shown in Figure 2.
Figure 2  The acceleration of the head during and after a 10-ms collision
Suppose the physical characteristics of the crash test dummy accurately represent those of a human.  What is the expected injury of the impact shown in Figure 2 if the head accelerated to 10 m/s at the end of the impact?

A)No injury
B)TBI and no skull fracture
C)Skull fracture and no TBI
D)TBI and skull fracture

Question 29

Passage
A traumatic brain injury (TBI) is a form of brain injury caused by an external physical force.  In addition to direct injury at the site of an impact, the rapid acceleration-deceleration of the head may cause the brain to move within the skull and result in injury to the part of the brain opposite the impact site.  This is known as a contrecoup injury.If an impact to the head also results in a skull fracture, the injury is classified as an open TBI.  If there is no skull fracture, the injury is classified as a closed TBI.  The type of TBI can be predicted from the collision duration and the average acceleration of the head.  The thresholds for open and closed TBI are shown in Figure 1.
Figure 1  Thresholds for open and closed TBIIn an experiment to study head collisions with projectiles, researchers equipped the head of a crash test dummy with sensors that measured acceleration on multiple axes.  The crash test dummy was stationary before its head was subjected to controlled collisions with incoming projectiles of varying mass and impact velocity.  The linear acceleration of the crash test dummy's head was recorded during and after the impact.  The results for a trial in which the impact lasted for 10 ms are shown in Figure 2.
Figure 2  The acceleration of the head during and after a 10-ms collision
In the range from 0 to 10 ms in Figure 2, which of the following represents the velocity of the head at 10 ms?

A)The length of the curve
B)The area under the curve
C)The maximum height of the curve
D)The maximum slope of the curve

Question 30

Passage
The electric capacitance of biological tissues serves as the basis for numerous medical technologies.  For example, dielectric spectroscopy glucose reading (DSGR) is a noninvasive diagnostic technique that uses the electric capacitance of blood to estimate blood glucose levels.A DSGR device records the electric current that results from applying a voltage source to the skin and underlying blood vessels.  DSGR can be modeled by the circuit shown in Figure 1, in which V represents the applied potential, C_B represents the capacitance of the blood, and R_E, R_D, and R_B represent the electrical resistances of the epidermis, the dermis, and the blood, respectively.
Figure 1  DSGR circuit model including skin and superficial blood vesselThe capacitance of charged blood may be explained by red blood cell membranes acting as physical barriers that separate electrons introduced into the blood from positively charged ions in the red blood cell cytoplasm.  The dielectric constant k of red blood cell membranes varies with glucose concentration (Figure 2) because glucose uptake by red blood cells alters the activity of membrane-bound proteins that regulate the flow of ions into and out of the cell.
Figure 2  Blood dielectric constant vs blood glucose concentrationDSGR readings vary with blood glucose concentration because the time needed to fully charge the blood is related to total blood capacitance.  However, interpreting DSGR readings may be complicated by changes in biological variables other than blood capacitance.  For example, the resistivity of blood varies in accordance with osmolarity such that changes in diet or hydration status influence the current measured by DSGR devices.
Livshits, L. et al.  Dielectric response of biconcave erythrocyte membranes to D- and L-glucose.  J. Phys. D: Appl. Phys. 40 (2007), 15-19.
To simplify calculations, mathematical models of DSGR can be generated that replace R_E and R_D in Figure 1 with an equivalent resistor R_eq.  The mathematical expression for R_eq is:

A)R_E + R_D
B)R_E ∙ R_D
C)(R_E + R_D)/(R_E ∙ R_D)
D)(R_E ∙ R_D)/(R_E + R_D)

Question 31

Passage
For a person with perfect vision, light from an object is properly refracted by the eye lens to converge on a single point at the retina, forming a clear image of the object.  Vision defects result from eye shape abnormalities or errors in the refractive power of the eye lens.  Myopia (nearsightedness) occurs when light from a distant object is incorrectly focused in front of the retina.  Hyperopia (farsightedness) occurs when light rays from a nearby object are focused beyond the retina.Many optical techniques are available to measure the refractive error of an individual to determine the necessary correction.  Photorefraction is a photographic technique often used with young children because it does not require the individual to be still for a lengthy duration.  When the patient is looking at the camera, a flash photograph is taken of the eye to determine the amount of light that is reflected off the retina and captured by the camera lens.In healthy eyes, all the light from the flash that enters the eye is reflected off the retina and returns back to the camera's light source.  Because the camera lens does not receive this light, the pupil is completely dark in the resulting image.  A myopic eye cannot properly focus the light at the retina.  Due to the geometry of the eye and its lens, some of the light is reflected to the top portion of the camera lens.  The camera captures an image of a pupil with a crescent of light at the top.  In a hyperopic eye, the crescent appears at the bottom of the pupil.  Ray diagrams for photorefraction are shown in Figure 1.
Figure 1  Paths of light in photorefraction for different eyes:  (A) Healthy, (B) Myopic, and (C) Hyperopic.
HC. Howland, "Optics of photorefraction: orthogonal and isotropic methods." ©1983 Optical Society of America.
What is the camera lens' refractive index if incident light 50° from the normal is refracted to 35° from the normal?

A)sin 50°/sin 35°
B)sin 35°/sin 50°
C)1/sin 50°
D)1/sin 35°

Question 32

Passage
For a person with perfect vision, light from an object is properly refracted by the eye lens to converge on a single point at the retina, forming a clear image of the object.  Vision defects result from eye shape abnormalities or errors in the refractive power of the eye lens.  Myopia (nearsightedness) occurs when light from a distant object is incorrectly focused in front of the retina.  Hyperopia (farsightedness) occurs when light rays from a nearby object are focused beyond the retina.Many optical techniques are available to measure the refractive error of an individual to determine the necessary correction.  Photorefraction is a photographic technique often used with young children because it does not require the individual to be still for a lengthy duration.  When the patient is looking at the camera, a flash photograph is taken of the eye to determine the amount of light that is reflected off the retina and captured by the camera lens.In healthy eyes, all the light from the flash that enters the eye is reflected off the retina and returns back to the camera's light source.  Because the camera lens does not receive this light, the pupil is completely dark in the resulting image.  A myopic eye cannot properly focus the light at the retina.  Due to the geometry of the eye and its lens, some of the light is reflected to the top portion of the camera lens.  The camera captures an image of a pupil with a crescent of light at the top.  In a hyperopic eye, the crescent appears at the bottom of the pupil.  Ray diagrams for photorefraction are shown in Figure 1.
Figure 1  Paths of light in photorefraction for different eyes:  (A) Healthy, (B) Myopic, and (C) Hyperopic.
HC. Howland, "Optics of photorefraction: orthogonal and isotropic methods." ©1983 Optical Society of America.
An object is located at a distance of 2 focal lengths from the center of a converging lens.  What is the ratio of the height of the image to the height of the object?

A)1:1
B)1:2
C)1:3
D)No image is formed.

Question 33

Passage
A traumatic brain injury (TBI) is a form of brain injury caused by an external physical force.  In addition to direct injury at the site of an impact, the rapid acceleration-deceleration of the head may cause the brain to move within the skull and result in injury to the part of the brain opposite the impact site.  This is known as a contrecoup injury.If an impact to the head also results in a skull fracture, the injury is classified as an open TBI.  If there is no skull fracture, the injury is classified as a closed TBI.  The type of TBI can be predicted from the collision duration and the average acceleration of the head.  The thresholds for open and closed TBI are shown in Figure 1.
Figure 1  Thresholds for open and closed TBIIn an experiment to study head collisions with projectiles, researchers equipped the head of a crash test dummy with sensors that measured acceleration on multiple axes.  The crash test dummy was stationary before its head was subjected to controlled collisions with incoming projectiles of varying mass and impact velocity.  The linear acceleration of the crash test dummy's head was recorded during and after the impact.  The results for a trial in which the impact lasted for 10 ms are shown in Figure 2.
Figure 2  The acceleration of the head during and after a 10-ms collision
When a stationary head is hit by a moving projectile, a contrecoup injury is likely to occur due to:

A)the inertia of the brain.
B)the weight of the skull.
C)the center of mass of the head.
D)the potential energy of the projectile.

Question 34

Passage
The electric capacitance of biological tissues serves as the basis for numerous medical technologies.  For example, dielectric spectroscopy glucose reading (DSGR) is a noninvasive diagnostic technique that uses the electric capacitance of blood to estimate blood glucose levels.A DSGR device records the electric current that results from applying a voltage source to the skin and underlying blood vessels.  DSGR can be modeled by the circuit shown in Figure 1, in which V represents the applied potential, C_B represents the capacitance of the blood, and R_E, R_D, and R_B represent the electrical resistances of the epidermis, the dermis, and the blood, respectively.
Figure 1  DSGR circuit model including skin and superficial blood vesselThe capacitance of charged blood may be explained by red blood cell membranes acting as physical barriers that separate electrons introduced into the blood from positively charged ions in the red blood cell cytoplasm.  The dielectric constant k of red blood cell membranes varies with glucose concentration (Figure 2) because glucose uptake by red blood cells alters the activity of membrane-bound proteins that regulate the flow of ions into and out of the cell.
Figure 2  Blood dielectric constant vs blood glucose concentrationDSGR readings vary with blood glucose concentration because the time needed to fully charge the blood is related to total blood capacitance.  However, interpreting DSGR readings may be complicated by changes in biological variables other than blood capacitance.  For example, the resistivity of blood varies in accordance with osmolarity such that changes in diet or hydration status influence the current measured by DSGR devices.
Livshits, L. et al.  Dielectric response of biconcave erythrocyte membranes to D- and L-glucose.  J. Phys. D: Appl. Phys. 40 (2007), 15-19.
When dietary sodium intake increases, the electric current measured by a DSGR device also increases.  Current increases because:

A)blood pressure energy is converted into electric potential energy.
B)the accumulation of positively charged ions causes blood glucose to precipitate.
C)electrolytes within blood transport electric charge.
D)alterations in red blood cell shape increase capacitance.

Question 35

Passage
The electric capacitance of biological tissues serves as the basis for numerous medical technologies.  For example, dielectric spectroscopy glucose reading (DSGR) is a noninvasive diagnostic technique that uses the electric capacitance of blood to estimate blood glucose levels.A DSGR device records the electric current that results from applying a voltage source to the skin and underlying blood vessels.  DSGR can be modeled by the circuit shown in Figure 1, in which V represents the applied potential, C_B represents the capacitance of the blood, and R_E, R_D, and R_B represent the electrical resistances of the epidermis, the dermis, and the blood, respectively.
Figure 1  DSGR circuit model including skin and superficial blood vesselThe capacitance of charged blood may be explained by red blood cell membranes acting as physical barriers that separate electrons introduced into the blood from positively charged ions in the red blood cell cytoplasm.  The dielectric constant k of red blood cell membranes varies with glucose concentration (Figure 2) because glucose uptake by red blood cells alters the activity of membrane-bound proteins that regulate the flow of ions into and out of the cell.
Figure 2  Blood dielectric constant vs blood glucose concentrationDSGR readings vary with blood glucose concentration because the time needed to fully charge the blood is related to total blood capacitance.  However, interpreting DSGR readings may be complicated by changes in biological variables other than blood capacitance.  For example, the resistivity of blood varies in accordance with osmolarity such that changes in diet or hydration status influence the current measured by DSGR devices.
Livshits, L. et al.  Dielectric response of biconcave erythrocyte membranes to D- and L-glucose.  J. Phys. D: Appl. Phys. 40 (2007), 15-19.
Which of the following statements best describes the behavior of the circuit in Figure 1 when the fully charged capacitor (comprising red blood cells) is discharged?

A)The electric currents through R_B and R_E are equal because the resistors are in series.
B)The voltage drops across R_B and R_E are equal because the resistors are in parallel.
C)The electric current through R_B exceeds that through R_E because the capacitor is fully charged.
D)Both the current and voltage drop across R_B and R_E are equal because the same power source is used.

Question 36

Passage
For a person with perfect vision, light from an object is properly refracted by the eye lens to converge on a single point at the retina, forming a clear image of the object.  Vision defects result from eye shape abnormalities or errors in the refractive power of the eye lens.  Myopia (nearsightedness) occurs when light from a distant object is incorrectly focused in front of the retina.  Hyperopia (farsightedness) occurs when light rays from a nearby object are focused beyond the retina.Many optical techniques are available to measure the refractive error of an individual to determine the necessary correction.  Photorefraction is a photographic technique often used with young children because it does not require the individual to be still for a lengthy duration.  When the patient is looking at the camera, a flash photograph is taken of the eye to determine the amount of light that is reflected off the retina and captured by the camera lens.In healthy eyes, all the light from the flash that enters the eye is reflected off the retina and returns back to the camera's light source.  Because the camera lens does not receive this light, the pupil is completely dark in the resulting image.  A myopic eye cannot properly focus the light at the retina.  Due to the geometry of the eye and its lens, some of the light is reflected to the top portion of the camera lens.  The camera captures an image of a pupil with a crescent of light at the top.  In a hyperopic eye, the crescent appears at the bottom of the pupil.  Ray diagrams for photorefraction are shown in Figure 1.
Figure 1  Paths of light in photorefraction for different eyes:  (A) Healthy, (B) Myopic, and (C) Hyperopic.
HC. Howland, "Optics of photorefraction: orthogonal and isotropic methods." ©1983 Optical Society of America.
The image of an object projected onto a fixed screen through a lens using red light is clear and focused.  Using the same set-up, the image is slightly unfocused when violet light is used.  This is because violet light:

A)refracts more than red light.
B)is more polarized than red light.
C)is unaffected by spherical aberrations.
D)has greater phase shifts in glass.

Question 37

Passage
For a person with perfect vision, light from an object is properly refracted by the eye lens to converge on a single point at the retina, forming a clear image of the object.  Vision defects result from eye shape abnormalities or errors in the refractive power of the eye lens.  Myopia (nearsightedness) occurs when light from a distant object is incorrectly focused in front of the retina.  Hyperopia (farsightedness) occurs when light rays from a nearby object are focused beyond the retina.Many optical techniques are available to measure the refractive error of an individual to determine the necessary correction.  Photorefraction is a photographic technique often used with young children because it does not require the individual to be still for a lengthy duration.  When the patient is looking at the camera, a flash photograph is taken of the eye to determine the amount of light that is reflected off the retina and captured by the camera lens.In healthy eyes, all the light from the flash that enters the eye is reflected off the retina and returns back to the camera's light source.  Because the camera lens does not receive this light, the pupil is completely dark in the resulting image.  A myopic eye cannot properly focus the light at the retina.  Due to the geometry of the eye and its lens, some of the light is reflected to the top portion of the camera lens.  The camera captures an image of a pupil with a crescent of light at the top.  In a hyperopic eye, the crescent appears at the bottom of the pupil.  Ray diagrams for photorefraction are shown in Figure 1.
Figure 1  Paths of light in photorefraction for different eyes:  (A) Healthy, (B) Myopic, and (C) Hyperopic.
HC. Howland, "Optics of photorefraction: orthogonal and isotropic methods." ©1983 Optical Society of America.
Photorefraction with a camera at a distance of 50 cm away from a child produces a completely dark image of the pupil.  If the child's retina is 2.5 cm from the eye lens, what is the lens strength of the eye?  (Note:  Use the thin lens formula, S = 1/o + 1/i.)

A)38 D
B)42 D
C)48 D
D)52 D

Question 38

Passage
The humerus bone in the upper arm and the radius bone in the lower arm can be modeled as a lever with the elbow joint as the pivot point.  Movement about the elbow results from a combination of internal and external forces acting on these bones.  The primary internal force is generated from contractions of skeletal muscles; a 1-cm² cross-sectional area of skeletal muscle can generate a maximum of 7 × 10⁶ dynes of force (1 dyn = 1 g⋅cm/s²).  Friction between the humerus and the radius at the elbow is another internal force that can affect arm movements.  As people age, cartilage degeneration decreases the lubrication between bones, which increases the coefficients of static and kinetic friction.The contraction of the biceps, a skeletal muscle in the upper arm, exerts a pulling force on the radius in the lower arm.  If the torque generated by this muscle exceeds that of any opposing internal and external forces, the arm curls about the elbow.  This specific type of movement is known as a concentric muscle contraction.The following experiments were performed with a 30-year-old male subject.  Electrodes were placed around the subject's biceps and attached to an electromyograph, a device that measures the electrical activity of skeletal muscle contractions.  The estimated weight of the subject's lower arm is 45 N, and the subject's lower arm segments to the elbow are shown in Table 1.Table 1  Lower Arm Segment Lengths
 Experiment 1The subject kept his entire arm stationary and in a fixed position while holding balls of varying masses.  The upper arm was perpendicular to the ground, and the lower arm was parallel to the ground (Figure 1).
Figure 1  The fixed position of the arm during Experiment 1Experiment 2The subject kept his upper arm stationary and perpendicular to the ground while lifting and lowering balls of varying masses.
Adapted from N. Ozkaya, Fundamentals of Biomechanics. (C) 2016 Springer.
What is the maximum pressure in N/m² generated by skeletal muscles?

A)7 × 10³ N/m²
B)7 × 10⁵ N/m²
C)7 × 10⁶ N/m²
D)7 × 10⁹ N/m²

Question 39

Passage
The humerus bone in the upper arm and the radius bone in the lower arm can be modeled as a lever with the elbow joint as the pivot point.  Movement about the elbow results from a combination of internal and external forces acting on these bones.  The primary internal force is generated from contractions of skeletal muscles; a 1-cm² cross-sectional area of skeletal muscle can generate a maximum of 7 × 10⁶ dynes of force (1 dyn = 1 g⋅cm/s²).  Friction between the humerus and the radius at the elbow is another internal force that can affect arm movements.  As people age, cartilage degeneration decreases the lubrication between bones, which increases the coefficients of static and kinetic friction.The contraction of the biceps, a skeletal muscle in the upper arm, exerts a pulling force on the radius in the lower arm.  If the torque generated by this muscle exceeds that of any opposing internal and external forces, the arm curls about the elbow.  This specific type of movement is known as a concentric muscle contraction.The following experiments were performed with a 30-year-old male subject.  Electrodes were placed around the subject's biceps and attached to an electromyograph, a device that measures the electrical activity of skeletal muscle contractions.  The estimated weight of the subject's lower arm is 45 N, and the subject's lower arm segments to the elbow are shown in Table 1.Table 1  Lower Arm Segment Lengths
 Experiment 1The subject kept his entire arm stationary and in a fixed position while holding balls of varying masses.  The upper arm was perpendicular to the ground, and the lower arm was parallel to the ground (Figure 1).
Figure 1  The fixed position of the arm during Experiment 1Experiment 2The subject kept his upper arm stationary and perpendicular to the ground while lifting and lowering balls of varying masses.
Adapted from N. Ozkaya, Fundamentals of Biomechanics. (C) 2016 Springer.
Suppose the subject is holding a 4-kg ball during Experiment 1.  Ignoring friction, what is the force exerted by the biceps?  (Note: Use g = 10 m/s².)

A)85 N
B)340 N
C)700 N
D)2,100 N

Question 40

Passage
A traumatic brain injury (TBI) is a form of brain injury caused by an external physical force.  In addition to direct injury at the site of an impact, the rapid acceleration-deceleration of the head may cause the brain to move within the skull and result in injury to the part of the brain opposite the impact site.  This is known as a contrecoup injury.If an impact to the head also results in a skull fracture, the injury is classified as an open TBI.  If there is no skull fracture, the injury is classified as a closed TBI.  The type of TBI can be predicted from the collision duration and the average acceleration of the head.  The thresholds for open and closed TBI are shown in Figure 1.
Figure 1  Thresholds for open and closed TBIIn an experiment to study head collisions with projectiles, researchers equipped the head of a crash test dummy with sensors that measured acceleration on multiple axes.  The crash test dummy was stationary before its head was subjected to controlled collisions with incoming projectiles of varying mass and impact velocity.  The linear acceleration of the crash test dummy's head was recorded during and after the impact.  The results for a trial in which the impact lasted for 10 ms are shown in Figure 2.
Figure 2  The acceleration of the head during and after a 10-ms collision
If a baseball traveling at 20 m/s strikes a player running at 5 m/s, what is the difference between the minimum and maximum possible relative velocities between the ball and the player?

A)10 m/s
B)15 m/s
C)20 m/s
D)25 m/s

Question 41

Passage
The humerus bone in the upper arm and the radius bone in the lower arm can be modeled as a lever with the elbow joint as the pivot point.  Movement about the elbow results from a combination of internal and external forces acting on these bones.  The primary internal force is generated from contractions of skeletal muscles; a 1-cm² cross-sectional area of skeletal muscle can generate a maximum of 7 × 10⁶ dynes of force (1 dyn = 1 g⋅cm/s²).  Friction between the humerus and the radius at the elbow is another internal force that can affect arm movements.  As people age, cartilage degeneration decreases the lubrication between bones, which increases the coefficients of static and kinetic friction.The contraction of the biceps, a skeletal muscle in the upper arm, exerts a pulling force on the radius in the lower arm.  If the torque generated by this muscle exceeds that of any opposing internal and external forces, the arm curls about the elbow.  This specific type of movement is known as a concentric muscle contraction.The following experiments were performed with a 30-year-old male subject.  Electrodes were placed around the subject's biceps and attached to an electromyograph, a device that measures the electrical activity of skeletal muscle contractions.  The estimated weight of the subject's lower arm is 45 N, and the subject's lower arm segments to the elbow are shown in Table 1.Table 1  Lower Arm Segment Lengths
 Experiment 1The subject kept his entire arm stationary and in a fixed position while holding balls of varying masses.  The upper arm was perpendicular to the ground, and the lower arm was parallel to the ground (Figure 1).
Figure 1  The fixed position of the arm during Experiment 1Experiment 2The subject kept his upper arm stationary and perpendicular to the ground while lifting and lowering balls of varying masses.
Adapted from N. Ozkaya, Fundamentals of Biomechanics. (C) 2016 Springer.
Which of the following graphs shows the relationship between the torque generated by the weight of the ball and the angle the biceps makes with the lower arm in Experiment 2?

A)
B)
C)
D)

Question 42

Passage
In mass spectrometry, a sample's molecules are ionized in a vacuum and then exposed to a uniform electric field created by a high-voltage plate in the acceleration chamber.  The electric field accelerates the ions until they arrive at the next section of the device, designated as the separation chamber.  In this section, the drifting ions are sorted by their mass-to-charge ratio (m/q).The separation chamber in a time-of-flight mass spectrometer (TOF-MS) is linear and has no electric or magnetic fields.  The ions travel at a constant velocity through the chamber until they reach the detector.  The time it takes for an ion to reach the detector depends on its m/q ratio.
Figure 1  Time-of-flight mass spectrometerA magnetic sector mass spectrometer (MS-MS) has a curved separation chamber where a magnetic field is generated.  The magnetic field exerts a centripetal force on drifting ions, bending their trajectories into curved paths.  The radius of the curvature depends on the ion's m/q.
Figure 2  Magnetic sector mass spectrometerThe centripetal force (F) acting on a particle can be determined from its mass (m) and velocity (v) and the radius (r) of the curved path:F = mv²/rEquation 1
What is the magnitude of the electric field generated in the acceleration chamber if the potential difference is 3,000 V over a distance of 50 cm?

A)1.5 kN/C
B)3.0 kN/C
C)4.5 kN/C
D)6.0 kN/C

Question 43

Passage
In mass spectrometry, a sample's molecules are ionized in a vacuum and then exposed to a uniform electric field created by a high-voltage plate in the acceleration chamber.  The electric field accelerates the ions until they arrive at the next section of the device, designated as the separation chamber.  In this section, the drifting ions are sorted by their mass-to-charge ratio (m/q).The separation chamber in a time-of-flight mass spectrometer (TOF-MS) is linear and has no electric or magnetic fields.  The ions travel at a constant velocity through the chamber until they reach the detector.  The time it takes for an ion to reach the detector depends on its m/q ratio.
Figure 1  Time-of-flight mass spectrometerA magnetic sector mass spectrometer (MS-MS) has a curved separation chamber where a magnetic field is generated.  The magnetic field exerts a centripetal force on drifting ions, bending their trajectories into curved paths.  The radius of the curvature depends on the ion's m/q.
Figure 2  Magnetic sector mass spectrometerThe centripetal force (F) acting on a particle can be determined from its mass (m) and velocity (v) and the radius (r) of the curved path:F = mv²/rEquation 1
Which expression gives the ion's radius of curvature in a magnetic field EM_/_ for an ion with a mass of m, charge of q, and velocity of v?

A)r = (m/q)(v²/B)
B)r = (m/q)(v/B)
C)r = (q/m)(v²/B)
D)r = (q/m)(v/B)

Question 44

Passage
When present in the bloodstream above a threshold partial pressure, a general anesthetic blocks the sensation of pain, induces a state of unconsciousness, and causes muscle paralysis.  Many anesthetic agents are administered in their gaseous phase and are absorbed into the bloodstream through the lungs.  The rate of diffusion V_gas of an anesthetic across the alveolar membrane with a surface area A and a thickness T is described by the Fick law of diffusion:
Vgas=DAΔPTEquation 1where D is the diffusion coefficient specific for the gas and ΔP is the partial pressure difference across the membrane.An inhaled anesthetic is described by its blood-gas partition coefficient, the ratio of the anesthetic's concentration in the blood to its concentration in the lungs when the partial pressures are equal.  The concentration C of an anesthetic gas dissolved in blood is described by the Henry law of solubility:
C=kHPgasEquation 2where k_H is the solubility constant specific for the gas and P_gas is the partial pressure of the gas.Due to the paralytic effects of general anesthetics, mechanical ventilators are usually necessary to assist a patient's breathing during surgery.  Positive-pressure ventilators are noninvasive and use external pumps to induce inspiration by forcing air into the lungs through a ventilation mask.  Despite the paralytic effects of general anesthesia, patients are often capable of expiration without the active aid of a mechanical ventilator.
A positive pressure mechanical ventilator most likely inflates the lungs by directly:

A)increasing intrapleural pressure.
B)decreasing intrapleural pressure.
C)increasing alveolar pressure.
D)decreasing alveolar pressure.

Question 45

Passage
In mass spectrometry, a sample's molecules are ionized in a vacuum and then exposed to a uniform electric field created by a high-voltage plate in the acceleration chamber.  The electric field accelerates the ions until they arrive at the next section of the device, designated as the separation chamber.  In this section, the drifting ions are sorted by their mass-to-charge ratio (m/q).The separation chamber in a time-of-flight mass spectrometer (TOF-MS) is linear and has no electric or magnetic fields.  The ions travel at a constant velocity through the chamber until they reach the detector.  The time it takes for an ion to reach the detector depends on its m/q ratio.
Figure 1  Time-of-flight mass spectrometerA magnetic sector mass spectrometer (MS-MS) has a curved separation chamber where a magnetic field is generated.  The magnetic field exerts a centripetal force on drifting ions, bending their trajectories into curved paths.  The radius of the curvature depends on the ion's m/q.
Figure 2  Magnetic sector mass spectrometerThe centripetal force (F) acting on a particle can be determined from its mass (m) and velocity (v) and the radius (r) of the curved path:F = mv²/rEquation 1
When ions X and Y are analyzed in a TOF-MS, ion Y took more time to reach the detector.  Which ion will be observed to have the smaller radius of curvature in MS-MS?

A)Ion X
B)Ion Y
C)They will have the same radius of curvature
D)Neither ion will curve in MS-MS

Question 46

Passage
In mass spectrometry, a sample's molecules are ionized in a vacuum and then exposed to a uniform electric field created by a high-voltage plate in the acceleration chamber.  The electric field accelerates the ions until they arrive at the next section of the device, designated as the separation chamber.  In this section, the drifting ions are sorted by their mass-to-charge ratio (m/q).The separation chamber in a time-of-flight mass spectrometer (TOF-MS) is linear and has no electric or magnetic fields.  The ions travel at a constant velocity through the chamber until they reach the detector.  The time it takes for an ion to reach the detector depends on its m/q ratio.
Figure 1  Time-of-flight mass spectrometerA magnetic sector mass spectrometer (MS-MS) has a curved separation chamber where a magnetic field is generated.  The magnetic field exerts a centripetal force on drifting ions, bending their trajectories into curved paths.  The radius of the curvature depends on the ion's m/q.
Figure 2  Magnetic sector mass spectrometerThe centripetal force (F) acting on a particle can be determined from its mass (m) and velocity (v) and the radius (r) of the curved path:F = mv²/rEquation 1
Which of the following best describes the high voltage plate if it accelerates positive ions away from it?

A)It is positively charged, and its electric field lines point away from it.
B)It is positively charged, and its electric field lines point toward it.
C)It is negatively charged, and its electric field lines point away from it.
D)It is negatively charged, and its electric field lines point toward it.

Question 47

Passage
The effects of gravity are effectively negated if an object is in free fall.  For example, an object orbiting the Earth experiences an apparent weightlessness known as microgravity.  Because the human body evolved under the influence of Earth's gravity, human physiology undergoes several changes in microgravity environments.  Puffy face syndrome (PFS) occurs when an astronaut's extracellular fluid shifts toward upper body regions, resulting in facial bulging and leg shrinkage.  Elongation of the spinal column also occurs as intervertebral discs (spinal cartilage) decompress, making astronauts up to 6 cm taller.Researchers simulated microgravity-induced spinal elongation on Earth by suspending 50 volunteers by the arms, holding each above the ground in an upright position.  The thickness of each intervertebral disc was measured prior to and following 10 minutes of suspension.  Researchers then compared the percentage change in intervertebral disc thickness to similar measurements recorded in microgravity, as shown in Figure 1.
Figure 1  Percentage change in intervertebral disc thicknessIn theory, spinal elongation would also occur in reduced-gravity environments like the surface of the Moon, where the acceleration of gravity is one-sixth that observed on the Earth's surface.
An astronaut drifts through space alongside the edge of a spaceship.  The astronaut moves as a rigid body with constant velocity and no rotation.  Which of the following occurs when the astronaut strikes a protruding portion of the spaceship with her foot?  The astronaut:

A)slows down and continues along her original path with no rotation.
B)turns upside down and slowly falls to the ship's surface.
C)continues along her original path while spinning about her center of mass.
D)stops, spins about the protrusion, and falls to the ship.

Question 48

Passage
In mass spectrometry, a sample's molecules are ionized in a vacuum and then exposed to a uniform electric field created by a high-voltage plate in the acceleration chamber.  The electric field accelerates the ions until they arrive at the next section of the device, designated as the separation chamber.  In this section, the drifting ions are sorted by their mass-to-charge ratio (m/q).The separation chamber in a time-of-flight mass spectrometer (TOF-MS) is linear and has no electric or magnetic fields.  The ions travel at a constant velocity through the chamber until they reach the detector.  The time it takes for an ion to reach the detector depends on its m/q ratio.
Figure 1  Time-of-flight mass spectrometerA magnetic sector mass spectrometer (MS-MS) has a curved separation chamber where a magnetic field is generated.  The magnetic field exerts a centripetal force on drifting ions, bending their trajectories into curved paths.  The radius of the curvature depends on the ion's m/q.
Figure 2  Magnetic sector mass spectrometerThe centripetal force (F) acting on a particle can be determined from its mass (m) and velocity (v) and the radius (r) of the curved path:F = mv²/rEquation 1
What is the force felt by a doubly ionized particle in a 2,000-N/C electric field?  (Note:  The charge of an electron is e = 1.6 × 10⁻¹⁹ C.)

A)1.6 × 10⁻²² N
B)3.2 × 10⁻²² N
C)3.2 × 10⁻¹⁶ N
D)6.4 × 10⁻¹⁶ N

Question 49

Passage
When present in the bloodstream above a threshold partial pressure, a general anesthetic blocks the sensation of pain, induces a state of unconsciousness, and causes muscle paralysis.  Many anesthetic agents are administered in their gaseous phase and are absorbed into the bloodstream through the lungs.  The rate of diffusion V_gas of an anesthetic across the alveolar membrane with a surface area A and a thickness T is described by the Fick law of diffusion:
Vgas=DAΔPTEquation 1where D is the diffusion coefficient specific for the gas and ΔP is the partial pressure difference across the membrane.An inhaled anesthetic is described by its blood-gas partition coefficient, the ratio of the anesthetic's concentration in the blood to its concentration in the lungs when the partial pressures are equal.  The concentration C of an anesthetic gas dissolved in blood is described by the Henry law of solubility:
C=kHPgasEquation 2where k_H is the solubility constant specific for the gas and P_gas is the partial pressure of the gas.Due to the paralytic effects of general anesthetics, mechanical ventilators are usually necessary to assist a patient's breathing during surgery.  Positive-pressure ventilators are noninvasive and use external pumps to induce inspiration by forcing air into the lungs through a ventilation mask.  Despite the paralytic effects of general anesthesia, patients are often capable of expiration without the active aid of a mechanical ventilator.
Which of the following characteristics would describe an inhalational anesthetic that is present in a relatively low concentration in the blood when it takes effect?

A)Relatively low solubility and a low blood-gas coefficient
B)Relatively low solubility and a high blood-gas coefficient
C)Relatively high solubility and a low blood-gas coefficient
D)Relatively high solubility and a high blood-gas coefficient

Question 50

Passage
The humerus bone in the upper arm and the radius bone in the lower arm can be modeled as a lever with the elbow joint as the pivot point.  Movement about the elbow results from a combination of internal and external forces acting on these bones.  The primary internal force is generated from contractions of skeletal muscles; a 1-cm² cross-sectional area of skeletal muscle can generate a maximum of 7 × 10⁶ dynes of force (1 dyn = 1 g⋅cm/s²).  Friction between the humerus and the radius at the elbow is another internal force that can affect arm movements.  As people age, cartilage degeneration decreases the lubrication between bones, which increases the coefficients of static and kinetic friction.The contraction of the biceps, a skeletal muscle in the upper arm, exerts a pulling force on the radius in the lower arm.  If the torque generated by this muscle exceeds that of any opposing internal and external forces, the arm curls about the elbow.  This specific type of movement is known as a concentric muscle contraction.The following experiments were performed with a 30-year-old male subject.  Electrodes were placed around the subject's biceps and attached to an electromyograph, a device that measures the electrical activity of skeletal muscle contractions.  The estimated weight of the subject's lower arm is 45 N, and the subject's lower arm segments to the elbow are shown in Table 1.Table 1  Lower Arm Segment Lengths
 Experiment 1The subject kept his entire arm stationary and in a fixed position while holding balls of varying masses.  The upper arm was perpendicular to the ground, and the lower arm was parallel to the ground (Figure 1).
Figure 1  The fixed position of the arm during Experiment 1Experiment 2The subject kept his upper arm stationary and perpendicular to the ground while lifting and lowering balls of varying masses.
Adapted from N. Ozkaya, Fundamentals of Biomechanics. (C) 2016 Springer.
Assuming the weight of the arm remains the same, how would the friction at the elbow change if the subject were to repeat the experiments 20 years later?

A)The static friction during Experiment 1 would increase.
B)The kinetic friction during Experiment 1 would increase.
C)The static friction during the lifting motion in Experiment 2 would decrease.
D)The kinetic friction during the lifting motion in Experiment 2 would decrease.

Question 51

Passage
The effects of gravity are effectively negated if an object is in free fall.  For example, an object orbiting the Earth experiences an apparent weightlessness known as microgravity.  Because the human body evolved under the influence of Earth's gravity, human physiology undergoes several changes in microgravity environments.  Puffy face syndrome (PFS) occurs when an astronaut's extracellular fluid shifts toward upper body regions, resulting in facial bulging and leg shrinkage.  Elongation of the spinal column also occurs as intervertebral discs (spinal cartilage) decompress, making astronauts up to 6 cm taller.Researchers simulated microgravity-induced spinal elongation on Earth by suspending 50 volunteers by the arms, holding each above the ground in an upright position.  The thickness of each intervertebral disc was measured prior to and following 10 minutes of suspension.  Researchers then compared the percentage change in intervertebral disc thickness to similar measurements recorded in microgravity, as shown in Figure 1.
Figure 1  Percentage change in intervertebral disc thicknessIn theory, spinal elongation would also occur in reduced-gravity environments like the surface of the Moon, where the acceleration of gravity is one-sixth that observed on the Earth's surface.
Which of the following statements explains the discrepancy between the microgravity data and the laboratory data for the experiment described in the passage?

A)In microgravity, gravitational forces were converted to tension.
B)In the laboratory setting, the weight of the body still acted on spinal cartilage.
C)The mass of the laboratory volunteers did not decrease.
D)Laboratory volunteers were not suspended upside-down to account for PFS.

Question 52

Passage
The effects of gravity are effectively negated if an object is in free fall.  For example, an object orbiting the Earth experiences an apparent weightlessness known as microgravity.  Because the human body evolved under the influence of Earth's gravity, human physiology undergoes several changes in microgravity environments.  Puffy face syndrome (PFS) occurs when an astronaut's extracellular fluid shifts toward upper body regions, resulting in facial bulging and leg shrinkage.  Elongation of the spinal column also occurs as intervertebral discs (spinal cartilage) decompress, making astronauts up to 6 cm taller.Researchers simulated microgravity-induced spinal elongation on Earth by suspending 50 volunteers by the arms, holding each above the ground in an upright position.  The thickness of each intervertebral disc was measured prior to and following 10 minutes of suspension.  Researchers then compared the percentage change in intervertebral disc thickness to similar measurements recorded in microgravity, as shown in Figure 1.
Figure 1  Percentage change in intervertebral disc thicknessIn theory, spinal elongation would also occur in reduced-gravity environments like the surface of the Moon, where the acceleration of gravity is one-sixth that observed on the Earth's surface.
Ignoring any attachments between the spinal discs and vertebrae, how would static friction between these anatomical structures compare for a person standing on the surface of the Moon to a person standing on the surface of the Earth?

A)It would be 6 times as great.
B)It would be approximately equal.
C)It would be 1/6 as great.
D)It would be 0.

Question 53

Passage
When present in the bloodstream above a threshold partial pressure, a general anesthetic blocks the sensation of pain, induces a state of unconsciousness, and causes muscle paralysis.  Many anesthetic agents are administered in their gaseous phase and are absorbed into the bloodstream through the lungs.  The rate of diffusion V_gas of an anesthetic across the alveolar membrane with a surface area A and a thickness T is described by the Fick law of diffusion:
Vgas=DAΔPTEquation 1where D is the diffusion coefficient specific for the gas and ΔP is the partial pressure difference across the membrane.An inhaled anesthetic is described by its blood-gas partition coefficient, the ratio of the anesthetic's concentration in the blood to its concentration in the lungs when the partial pressures are equal.  The concentration C of an anesthetic gas dissolved in blood is described by the Henry law of solubility:
C=kHPgasEquation 2where k_H is the solubility constant specific for the gas and P_gas is the partial pressure of the gas.Due to the paralytic effects of general anesthetics, mechanical ventilators are usually necessary to assist a patient's breathing during surgery.  Positive-pressure ventilators are noninvasive and use external pumps to induce inspiration by forcing air into the lungs through a ventilation mask.  Despite the paralytic effects of general anesthesia, patients are often capable of expiration without the active aid of a mechanical ventilator.
Many inhalational anesthetics are thought to increase surface tension effects in the alveoli.  Water with greater surface tension:

A)climbs farther in a narrow glass tube.
B)evaporates more quickly.
C)has weaker van der Waals forces.
D)creates droplets with smaller surface areas.

Question 54

Passage
The effects of gravity are effectively negated if an object is in free fall.  For example, an object orbiting the Earth experiences an apparent weightlessness known as microgravity.  Because the human body evolved under the influence of Earth's gravity, human physiology undergoes several changes in microgravity environments.  Puffy face syndrome (PFS) occurs when an astronaut's extracellular fluid shifts toward upper body regions, resulting in facial bulging and leg shrinkage.  Elongation of the spinal column also occurs as intervertebral discs (spinal cartilage) decompress, making astronauts up to 6 cm taller.Researchers simulated microgravity-induced spinal elongation on Earth by suspending 50 volunteers by the arms, holding each above the ground in an upright position.  The thickness of each intervertebral disc was measured prior to and following 10 minutes of suspension.  Researchers then compared the percentage change in intervertebral disc thickness to similar measurements recorded in microgravity, as shown in Figure 1.
Figure 1  Percentage change in intervertebral disc thicknessIn theory, spinal elongation would also occur in reduced-gravity environments like the surface of the Moon, where the acceleration of gravity is one-sixth that observed on the Earth's surface.
Provided that the initial velocity in both circumstances is identical, how much longer will an astronaut's vertical jumps last on the surface of the Moon compared to on the surface of the Earth?

A)1/6 as long
B)1/3 as long
C)3 times longer
D)6 times longer

Question 55

Passage
When present in the bloodstream above a threshold partial pressure, a general anesthetic blocks the sensation of pain, induces a state of unconsciousness, and causes muscle paralysis.  Many anesthetic agents are administered in their gaseous phase and are absorbed into the bloodstream through the lungs.  The rate of diffusion V_gas of an anesthetic across the alveolar membrane with a surface area A and a thickness T is described by the Fick law of diffusion:
Vgas=DAΔPTEquation 1where D is the diffusion coefficient specific for the gas and ΔP is the partial pressure difference across the membrane.An inhaled anesthetic is described by its blood-gas partition coefficient, the ratio of the anesthetic's concentration in the blood to its concentration in the lungs when the partial pressures are equal.  The concentration C of an anesthetic gas dissolved in blood is described by the Henry law of solubility:
C=kHPgasEquation 2where k_H is the solubility constant specific for the gas and P_gas is the partial pressure of the gas.Due to the paralytic effects of general anesthetics, mechanical ventilators are usually necessary to assist a patient's breathing during surgery.  Positive-pressure ventilators are noninvasive and use external pumps to induce inspiration by forcing air into the lungs through a ventilation mask.  Despite the paralytic effects of general anesthesia, patients are often capable of expiration without the active aid of a mechanical ventilator.
Which of the following graphs best depicts the anesthetic partial pressure along the length of the pulmonary capillaries when it is first administered?

A)
B)
C)
D)

Question 56

Passage
When present in the bloodstream above a threshold partial pressure, a general anesthetic blocks the sensation of pain, induces a state of unconsciousness, and causes muscle paralysis.  Many anesthetic agents are administered in their gaseous phase and are absorbed into the bloodstream through the lungs.  The rate of diffusion V_gas of an anesthetic across the alveolar membrane with a surface area A and a thickness T is described by the Fick law of diffusion:
Vgas=DAΔPTEquation 1where D is the diffusion coefficient specific for the gas and ΔP is the partial pressure difference across the membrane.An inhaled anesthetic is described by its blood-gas partition coefficient, the ratio of the anesthetic's concentration in the blood to its concentration in the lungs when the partial pressures are equal.  The concentration C of an anesthetic gas dissolved in blood is described by the Henry law of solubility:
C=kHPgasEquation 2where k_H is the solubility constant specific for the gas and P_gas is the partial pressure of the gas.Due to the paralytic effects of general anesthetics, mechanical ventilators are usually necessary to assist a patient's breathing during surgery.  Positive-pressure ventilators are noninvasive and use external pumps to induce inspiration by forcing air into the lungs through a ventilation mask.  Despite the paralytic effects of general anesthesia, patients are often capable of expiration without the active aid of a mechanical ventilator.
Unassisted expiration is possible under the effects of anesthesia due to:

A)pressure build-up due to the Venturi effect.
B)the elasticity of pulmonary tissue.
C)turbulent flow at high positive pressures.
D)energy stored in the diaphragm.

Question 57

Passage
When present in the bloodstream above a threshold partial pressure, a general anesthetic blocks the sensation of pain, induces a state of unconsciousness, and causes muscle paralysis.  Many anesthetic agents are administered in their gaseous phase and are absorbed into the bloodstream through the lungs.  The rate of diffusion V_gas of an anesthetic across the alveolar membrane with a surface area A and a thickness T is described by the Fick law of diffusion:
Vgas=DAΔPTEquation 1where D is the diffusion coefficient specific for the gas and ΔP is the partial pressure difference across the membrane.An inhaled anesthetic is described by its blood-gas partition coefficient, the ratio of the anesthetic's concentration in the blood to its concentration in the lungs when the partial pressures are equal.  The concentration C of an anesthetic gas dissolved in blood is described by the Henry law of solubility:
C=kHPgasEquation 2where k_H is the solubility constant specific for the gas and P_gas is the partial pressure of the gas.Due to the paralytic effects of general anesthetics, mechanical ventilators are usually necessary to assist a patient's breathing during surgery.  Positive-pressure ventilators are noninvasive and use external pumps to induce inspiration by forcing air into the lungs through a ventilation mask.  Despite the paralytic effects of general anesthesia, patients are often capable of expiration without the active aid of a mechanical ventilator.
An inhalational anesthetic administered to a patient has a rate of diffusion V_gas.  If the partial pressure difference is doubled and the membrane thickness is also doubled, what will be the new rate of diffusion?

A)V_gas/2
B)V_gas
C)2V_gas
D)4V_gas

Question 58

Passage
The effects of gravity are effectively negated if an object is in free fall.  For example, an object orbiting the Earth experiences an apparent weightlessness known as microgravity.  Because the human body evolved under the influence of Earth's gravity, human physiology undergoes several changes in microgravity environments.  Puffy face syndrome (PFS) occurs when an astronaut's extracellular fluid shifts toward upper body regions, resulting in facial bulging and leg shrinkage.  Elongation of the spinal column also occurs as intervertebral discs (spinal cartilage) decompress, making astronauts up to 6 cm taller.Researchers simulated microgravity-induced spinal elongation on Earth by suspending 50 volunteers by the arms, holding each above the ground in an upright position.  The thickness of each intervertebral disc was measured prior to and following 10 minutes of suspension.  Researchers then compared the percentage change in intervertebral disc thickness to similar measurements recorded in microgravity, as shown in Figure 1.
Figure 1  Percentage change in intervertebral disc thicknessIn theory, spinal elongation would also occur in reduced-gravity environments like the surface of the Moon, where the acceleration of gravity is one-sixth that observed on the Earth's surface.
According to the passage, which of the following changes as an astronaut leaves Earth's surface and enters orbit?

A)Magnitude of kinetic friction between the astronaut and nearby objects.
B)Astronaut center of mass.
C)Astronaut bodily inertia.
D)Magnitude of the gravitational force between the astronaut and the spacecraft.

Question 59

Passage
The effects of gravity are effectively negated if an object is in free fall.  For example, an object orbiting the Earth experiences an apparent weightlessness known as microgravity.  Because the human body evolved under the influence of Earth's gravity, human physiology undergoes several changes in microgravity environments.  Puffy face syndrome (PFS) occurs when an astronaut's extracellular fluid shifts toward upper body regions, resulting in facial bulging and leg shrinkage.  Elongation of the spinal column also occurs as intervertebral discs (spinal cartilage) decompress, making astronauts up to 6 cm taller.Researchers simulated microgravity-induced spinal elongation on Earth by suspending 50 volunteers by the arms, holding each above the ground in an upright position.  The thickness of each intervertebral disc was measured prior to and following 10 minutes of suspension.  Researchers then compared the percentage change in intervertebral disc thickness to similar measurements recorded in microgravity, as shown in Figure 1.
Figure 1  Percentage change in intervertebral disc thicknessIn theory, spinal elongation would also occur in reduced-gravity environments like the surface of the Moon, where the acceleration of gravity is one-sixth that observed on the Earth's surface.
A volunteer with a mass of 80 kg is suspended by his arms on Earth.  What is the approximate tension on lumbar disc 1?  (Note: The acceleration of gravity is g = 10 m/s²)

A)40 N
B)70 N
C)400 N
D)700 N

Question 60

Passage
In mass spectrometry, a sample's molecules are ionized in a vacuum and then exposed to a uniform electric field created by a high-voltage plate in the acceleration chamber.  The electric field accelerates the ions until they arrive at the next section of the device, designated as the separation chamber.  In this section, the drifting ions are sorted by their mass-to-charge ratio (m/q).The separation chamber in a time-of-flight mass spectrometer (TOF-MS) is linear and has no electric or magnetic fields.  The ions travel at a constant velocity through the chamber until they reach the detector.  The time it takes for an ion to reach the detector depends on its m/q ratio.
Figure 1  Time-of-flight mass spectrometerA magnetic sector mass spectrometer (MS-MS) has a curved separation chamber where a magnetic field is generated.  The magnetic field exerts a centripetal force on drifting ions, bending their trajectories into curved paths.  The radius of the curvature depends on the ion's m/q.
Figure 2  Magnetic sector mass spectrometerThe centripetal force (F) acting on a particle can be determined from its mass (m) and velocity (v) and the radius (r) of the curved path:F = mv²/rEquation 1
In the MS-MS separation chamber, the direction of the magnetic force on a moving ion is:

A)perpendicular to both the ion's velocity and the direction of the magnetic field.
B)perpendicular to the ion's velocity and parallel to the direction of the magnetic field.
C)parallel to both the ion's velocity and the direction of the magnetic field.
D)parallel to the ion's velocity and perpendicular to the direction of the magnetic field.

Question 61

Passage
In the event of end-stage heart failure, a left ventricular assist device (LVAD) can be used as a heart transplant bridge to keep a patient alive.  The first iterations of LVADs were pulsatile and mimicked the physiological pumping action of the heart (Figure 1).
Figure 1  A pulsatile-flow LVAD schematicA pulsatile-flow LVAD assists ventricular systole by mechanically pumping blood from a weakened left ventricle into the aorta through a pair of one-way valves.  The pressure differential ΔP generated by the pump is related to cardiac output (CO) and vascular resistance (VR):ΔP = CO × VREquation 1The efficiency and performance of the heart (or LVAD) can be determined by the patient's cardiac pressure-volume (PV) loop.  A cardiac PV loop plots the pressure and volume of the blood in the left ventricle throughout a single cardiac cycle (Figure 2).
Figure 2  Cardiac PV Loop of a pulsatile-flow LVADBlood pressure is often represented by only two numbers:  arterial systolic and diastolic pressures.  A more detailed representation of blood pressures is shown in a blood pressure profile, which graphs the blood pressure throughout the length of the different vessel groups (Figure 3).  Multiple pressure fluctuations are shown within a vessel because the pressure is traced across multiple cardiac cycles.
Figure 3  Blood pressure profile of the different vessels
In the above figure, an LVAD pump is placed at one end of a "U"-shaped container, and a force gauge is placed at the other end.  If the container is filled with an incompressible fluid, what is the ratio of the force measured by the force gauge to the force exerted by the LVAD?

A)1:4
B)1:2
C)1:1
D)4:1

Question 62

Passage
Sound waves propagate through many conducting structures in the ear before they are transduced into neuronal signals.  When sound waves reach the fluid-filled cochlea, they are detected by hair cells lining the basilar membrane.  The cochlear spiral can be modeled as a resonator system because each section of the basilar membrane is sensitive to a specific frequency (Figure 1).
Figure 1  Amplitude pattern of the basilar membrane for different frequenciesPresbycusis (age-related hearing loss) results from a combination of factors that lessens an individual's mechanical and/or neurological sensitivity to sound.  Pure tone audiometry (PTA) is used to determine an individual's ability to detect different sound frequencies and can be used to evaluate presbycusis.  A "pure" tone is characterized by a single sinusoidal waveform.  An audiogram plots the relative intensity required of a given frequency to be detected by the individual (Figure 2).
Figure 2  Audiogram of an elderly patient exhibiting presbycusis
In Figure 2, how does the hearing threshold intensity at 1,500 Hz compare to the threshold intensity at 2,000 Hz?

A)It is 30 times less intense.
B)It is 30 times more intense.
C)It is 1,000 times less intense.
D)It is 1,000 times more intense.

Question 63

Passage
Ultrasound is a technique that uses the propagation properties of high-frequency sound waves to construct images of internal organs or to measure blood flow velocity.  The shape and position of internal organs are resolved by measuring the return time of reflected ultrasound waves.  Similarly, blood flow velocity is resolved by measuring the Doppler shift of reflected ultrasound waves.  An ultrasound device consists of an array of piezoelectric crystals and an acoustic lens.  The piezoelectric crystals generate sound when an alternating voltage is applied, and the acoustic lens increases the transmission efficiency from the device to the body by reducing sound reflection at the skin.Ultrasound is performed using frequencies in the range of 2-15 MHz.  The lower ultrasound frequencies are used for deep abdomen and obstetric/gynecological imaging due to their greater penetrating ability.  The higher ultrasound frequencies have less penetrating ability but provide higher resolution, and therefore are used for blood flow measurements and the imaging of more superficial structures.  Detailed ultrasound penetration data is shown in Figure 1.
Figure 1  Penetration in soft tissue for three different ultrasound frequenciesSound waves propagate through soft tissue at an average speed of 1,500 m/s and through blood at 1,570 m/s.
Piezoelectric crystals likely create sound by:

A)rapidly expanding and contracting.
B)emitting high-energy photons.
C)generating heat waves.
D)sending pulses of electricity.

Question 64

Passage
Ultrasound is a technique that uses the propagation properties of high-frequency sound waves to construct images of internal organs or to measure blood flow velocity.  The shape and position of internal organs are resolved by measuring the return time of reflected ultrasound waves.  Similarly, blood flow velocity is resolved by measuring the Doppler shift of reflected ultrasound waves.  An ultrasound device consists of an array of piezoelectric crystals and an acoustic lens.  The piezoelectric crystals generate sound when an alternating voltage is applied, and the acoustic lens increases the transmission efficiency from the device to the body by reducing sound reflection at the skin.Ultrasound is performed using frequencies in the range of 2-15 MHz.  The lower ultrasound frequencies are used for deep abdomen and obstetric/gynecological imaging due to their greater penetrating ability.  The higher ultrasound frequencies have less penetrating ability but provide higher resolution, and therefore are used for blood flow measurements and the imaging of more superficial structures.  Detailed ultrasound penetration data is shown in Figure 1.
Figure 1  Penetration in soft tissue for three different ultrasound frequenciesSound waves propagate through soft tissue at an average speed of 1,500 m/s and through blood at 1,570 m/s.
How much farther will a 5 MHz signal penetrate compared to a 10 MHz signal when the initial intensity of each signal decreases by a factor of 100?

A)1 cm
B)2 cm
C)4 cm
D)10 cm

Question 65

Passage
Positron emission tomography (PET) is a medical imaging technique used for the detection of tumors and the evaluation of neurological functions.  A radiopharmaceutical (radioactive tracer) injected into a patient undergoes positive beta decay and emits a positron.  The positron undergoes an annihilation event with a nearby electron (<1 mm away), which emits a pair of 511 keV gamma ray photons traveling in opposite directions.  The gamma rays are detected by a ring of scintillation detectors surrounding the patient, as shown in Figure 1.  The difference in detection time between the two gamma rays from the same annihilation event is used to determine its location.  An image is constructed from data collected from multiple emission events.
Figure 1  Basic setup and process of positron emission tomographyScintillation, the emission of detectable light when excited electrons return to their ground state, occurs in crystals within the detectors due to the transfer of energy from the high energy gamma rays.  The wavelength of the emitted light depends exclusively on the type of scintillation material used (Table 1).Table 1  Common PET Scintillating Crystal Materials
The electrons in the scintillating crystals are excited through Compton scattering, a process in which a gamma ray photon acts as a particle, and transfers energy to an electron via collision.  Subsequently, the photon scatters (travels in a new direction) and its wavelength changes.  The percent change in the wavelength of the photon due to the energy loss is
Equation 1where θ is the angle between the scattered photon and electron.  Equation 1 is represented in Figure 2.
Figure 2  Percent change in photon wavelength due to Compton scattering

What is the frequency of the gamma rays emitted in PET?  (Note:  Use h = 4 × 10⁻¹⁵ eV⋅s.)

A)1.28 × 10²⁰ Hz
B)1.28 × 10¹⁷ Hz
C)2.44 × 10⁻⁹ Hz
D)2.44 × 10⁻¹² Hz

Question 66

Passage
Positron emission tomography (PET) is a medical imaging technique used for the detection of tumors and the evaluation of neurological functions.  A radiopharmaceutical (radioactive tracer) injected into a patient undergoes positive beta decay and emits a positron.  The positron undergoes an annihilation event with a nearby electron (<1 mm away), which emits a pair of 511 keV gamma ray photons traveling in opposite directions.  The gamma rays are detected by a ring of scintillation detectors surrounding the patient, as shown in Figure 1.  The difference in detection time between the two gamma rays from the same annihilation event is used to determine its location.  An image is constructed from data collected from multiple emission events.
Figure 1  Basic setup and process of positron emission tomographyScintillation, the emission of detectable light when excited electrons return to their ground state, occurs in crystals within the detectors due to the transfer of energy from the high energy gamma rays.  The wavelength of the emitted light depends exclusively on the type of scintillation material used (Table 1).Table 1  Common PET Scintillating Crystal Materials
The electrons in the scintillating crystals are excited through Compton scattering, a process in which a gamma ray photon acts as a particle, and transfers energy to an electron via collision.  Subsequently, the photon scatters (travels in a new direction) and its wavelength changes.  The percent change in the wavelength of the photon due to the energy loss is
Equation 1where θ is the angle between the scattered photon and electron.  Equation 1 is represented in Figure 2.
Figure 2  Percent change in photon wavelength due to Compton scattering

In which of the given scintillation materials will light travel the slowest?

A)Lu₂S₃:Ce
B)BGO
C)LSO
D)BaF₂:Ce

Question 67

Passage
In the event of end-stage heart failure, a left ventricular assist device (LVAD) can be used as a heart transplant bridge to keep a patient alive.  The first iterations of LVADs were pulsatile and mimicked the physiological pumping action of the heart (Figure 1).
Figure 1  A pulsatile-flow LVAD schematicA pulsatile-flow LVAD assists ventricular systole by mechanically pumping blood from a weakened left ventricle into the aorta through a pair of one-way valves.  The pressure differential ΔP generated by the pump is related to cardiac output (CO) and vascular resistance (VR):ΔP = CO × VREquation 1The efficiency and performance of the heart (or LVAD) can be determined by the patient's cardiac pressure-volume (PV) loop.  A cardiac PV loop plots the pressure and volume of the blood in the left ventricle throughout a single cardiac cycle (Figure 2).
Figure 2  Cardiac PV Loop of a pulsatile-flow LVADBlood pressure is often represented by only two numbers:  arterial systolic and diastolic pressures.  A more detailed representation of blood pressures is shown in a blood pressure profile, which graphs the blood pressure throughout the length of the different vessel groups (Figure 3).  Multiple pressure fluctuations are shown within a vessel because the pressure is traced across multiple cardiac cycles.
Figure 3  Blood pressure profile of the different vessels
The area enclosed by the cardiac PV loop is:

A)the cardiac output.
B)the work done.
C)the power of the LVAD.
D)the net pressure drop.

Question 68

Passage
In the event of end-stage heart failure, a left ventricular assist device (LVAD) can be used as a heart transplant bridge to keep a patient alive.  The first iterations of LVADs were pulsatile and mimicked the physiological pumping action of the heart (Figure 1).
Figure 1  A pulsatile-flow LVAD schematicA pulsatile-flow LVAD assists ventricular systole by mechanically pumping blood from a weakened left ventricle into the aorta through a pair of one-way valves.  The pressure differential ΔP generated by the pump is related to cardiac output (CO) and vascular resistance (VR):ΔP = CO × VREquation 1The efficiency and performance of the heart (or LVAD) can be determined by the patient's cardiac pressure-volume (PV) loop.  A cardiac PV loop plots the pressure and volume of the blood in the left ventricle throughout a single cardiac cycle (Figure 2).
Figure 2  Cardiac PV Loop of a pulsatile-flow LVADBlood pressure is often represented by only two numbers:  arterial systolic and diastolic pressures.  A more detailed representation of blood pressures is shown in a blood pressure profile, which graphs the blood pressure throughout the length of the different vessel groups (Figure 3).  Multiple pressure fluctuations are shown within a vessel because the pressure is traced across multiple cardiac cycles.
Figure 3  Blood pressure profile of the different vessels
If the pulsatile-flow LVAD in Figure 2 pumps with a frequency of 1.5 Hz, what is the volumetric flow rate of blood throughout the systemic circulatory system?

A)2,800 mL/min
B)6,300 mL/min
C)9,900 mL/min
D)10,800 mL/min

Question 69

Passage
In the event of end-stage heart failure, a left ventricular assist device (LVAD) can be used as a heart transplant bridge to keep a patient alive.  The first iterations of LVADs were pulsatile and mimicked the physiological pumping action of the heart (Figure 1).
Figure 1  A pulsatile-flow LVAD schematicA pulsatile-flow LVAD assists ventricular systole by mechanically pumping blood from a weakened left ventricle into the aorta through a pair of one-way valves.  The pressure differential ΔP generated by the pump is related to cardiac output (CO) and vascular resistance (VR):ΔP = CO × VREquation 1The efficiency and performance of the heart (or LVAD) can be determined by the patient's cardiac pressure-volume (PV) loop.  A cardiac PV loop plots the pressure and volume of the blood in the left ventricle throughout a single cardiac cycle (Figure 2).
Figure 2  Cardiac PV Loop of a pulsatile-flow LVADBlood pressure is often represented by only two numbers:  arterial systolic and diastolic pressures.  A more detailed representation of blood pressures is shown in a blood pressure profile, which graphs the blood pressure throughout the length of the different vessel groups (Figure 3).  Multiple pressure fluctuations are shown within a vessel because the pressure is traced across multiple cardiac cycles.
Figure 3  Blood pressure profile of the different vessels
If the radius of the outflow tube is 1 cm and the LVAD pump generates a pressure of 45 mm Hg, what is the velocity of blood through the outflow tube if peripheral resistance is 1 mm Hg⋅s⋅mL⁻¹?

A)45/π cm/s
B)45/π cm³/s
C)45 cm/s
D)45 cm³/s

Question 70

Passage
Sound waves propagate through many conducting structures in the ear before they are transduced into neuronal signals.  When sound waves reach the fluid-filled cochlea, they are detected by hair cells lining the basilar membrane.  The cochlear spiral can be modeled as a resonator system because each section of the basilar membrane is sensitive to a specific frequency (Figure 1).
Figure 1  Amplitude pattern of the basilar membrane for different frequenciesPresbycusis (age-related hearing loss) results from a combination of factors that lessens an individual's mechanical and/or neurological sensitivity to sound.  Pure tone audiometry (PTA) is used to determine an individual's ability to detect different sound frequencies and can be used to evaluate presbycusis.  A "pure" tone is characterized by a single sinusoidal waveform.  An audiogram plots the relative intensity required of a given frequency to be detected by the individual (Figure 2).
Figure 2  Audiogram of an elderly patient exhibiting presbycusis
Hearing loss due to loud environments can be mitigated with noise-canceling earphones, which generate a waveform that reduces the intensity of ambient noise through wave interference. For the above sound wave, the waveform generated for complete noise cancellation will be:

A)phase-shifted by half a wavelength.
B)flipped across the x-axis.
C)double the frequency.
D)the exact same wave.

Question 71

Passage
Positron emission tomography (PET) is a medical imaging technique used for the detection of tumors and the evaluation of neurological functions.  A radiopharmaceutical (radioactive tracer) injected into a patient undergoes positive beta decay and emits a positron.  The positron undergoes an annihilation event with a nearby electron (<1 mm away), which emits a pair of 511 keV gamma ray photons traveling in opposite directions.  The gamma rays are detected by a ring of scintillation detectors surrounding the patient, as shown in Figure 1.  The difference in detection time between the two gamma rays from the same annihilation event is used to determine its location.  An image is constructed from data collected from multiple emission events.
Figure 1  Basic setup and process of positron emission tomographyScintillation, the emission of detectable light when excited electrons return to their ground state, occurs in crystals within the detectors due to the transfer of energy from the high energy gamma rays.  The wavelength of the emitted light depends exclusively on the type of scintillation material used (Table 1).Table 1  Common PET Scintillating Crystal Materials
The electrons in the scintillating crystals are excited through Compton scattering, a process in which a gamma ray photon acts as a particle, and transfers energy to an electron via collision.  Subsequently, the photon scatters (travels in a new direction) and its wavelength changes.  The percent change in the wavelength of the photon due to the energy loss is
Equation 1where θ is the angle between the scattered photon and electron.  Equation 1 is represented in Figure 2.
Figure 2  Percent change in photon wavelength due to Compton scattering

Which scintillation crystal emits light with a wavelength outside the visible spectrum?

A)Lu₂S₃:Ce
B)BGO
C)LSO
D)BaF₂:Ce

Question 72

Passage
Positron emission tomography (PET) is a medical imaging technique used for the detection of tumors and the evaluation of neurological functions.  A radiopharmaceutical (radioactive tracer) injected into a patient undergoes positive beta decay and emits a positron.  The positron undergoes an annihilation event with a nearby electron (<1 mm away), which emits a pair of 511 keV gamma ray photons traveling in opposite directions.  The gamma rays are detected by a ring of scintillation detectors surrounding the patient, as shown in Figure 1.  The difference in detection time between the two gamma rays from the same annihilation event is used to determine its location.  An image is constructed from data collected from multiple emission events.
Figure 1  Basic setup and process of positron emission tomographyScintillation, the emission of detectable light when excited electrons return to their ground state, occurs in crystals within the detectors due to the transfer of energy from the high energy gamma rays.  The wavelength of the emitted light depends exclusively on the type of scintillation material used (Table 1).Table 1  Common PET Scintillating Crystal Materials
The electrons in the scintillating crystals are excited through Compton scattering, a process in which a gamma ray photon acts as a particle, and transfers energy to an electron via collision.  Subsequently, the photon scatters (travels in a new direction) and its wavelength changes.  The percent change in the wavelength of the photon due to the energy loss is
Equation 1where θ is the angle between the scattered photon and electron.  Equation 1 is represented in Figure 2.
Figure 2  Percent change in photon wavelength due to Compton scattering

If the angle between a Compton-scattered photon and an electron is 60°, what is the energy of the scattered photon in terms of the original energy E?

A)
B)
C)E
D)

Question 73

Passage
In the event of end-stage heart failure, a left ventricular assist device (LVAD) can be used as a heart transplant bridge to keep a patient alive.  The first iterations of LVADs were pulsatile and mimicked the physiological pumping action of the heart (Figure 1).
Figure 1  A pulsatile-flow LVAD schematicA pulsatile-flow LVAD assists ventricular systole by mechanically pumping blood from a weakened left ventricle into the aorta through a pair of one-way valves.  The pressure differential ΔP generated by the pump is related to cardiac output (CO) and vascular resistance (VR):ΔP = CO × VREquation 1The efficiency and performance of the heart (or LVAD) can be determined by the patient's cardiac pressure-volume (PV) loop.  A cardiac PV loop plots the pressure and volume of the blood in the left ventricle throughout a single cardiac cycle (Figure 2).
Figure 2  Cardiac PV Loop of a pulsatile-flow LVADBlood pressure is often represented by only two numbers:  arterial systolic and diastolic pressures.  A more detailed representation of blood pressures is shown in a blood pressure profile, which graphs the blood pressure throughout the length of the different vessel groups (Figure 3).  Multiple pressure fluctuations are shown within a vessel because the pressure is traced across multiple cardiac cycles.
Figure 3  Blood pressure profile of the different vessels
The mean arterial pressure (MAP) is used to approximate the average blood pressure of an individual's arteries:MAP = DP + (SP - DP)/3where DP is diastolic pressure and SP is systolic pressure.  What is the MAP for the blood pressure profile shown in Figure 3?

A)40 mm Hg
B)80 mm Hg
C)100 mm Hg
D)105 mm Hg

Question 74

Passage
In the event of end-stage heart failure, a left ventricular assist device (LVAD) can be used as a heart transplant bridge to keep a patient alive.  The first iterations of LVADs were pulsatile and mimicked the physiological pumping action of the heart (Figure 1).
Figure 1  A pulsatile-flow LVAD schematicA pulsatile-flow LVAD assists ventricular systole by mechanically pumping blood from a weakened left ventricle into the aorta through a pair of one-way valves.  The pressure differential ΔP generated by the pump is related to cardiac output (CO) and vascular resistance (VR):ΔP = CO × VREquation 1The efficiency and performance of the heart (or LVAD) can be determined by the patient's cardiac pressure-volume (PV) loop.  A cardiac PV loop plots the pressure and volume of the blood in the left ventricle throughout a single cardiac cycle (Figure 2).
Figure 2  Cardiac PV Loop of a pulsatile-flow LVADBlood pressure is often represented by only two numbers:  arterial systolic and diastolic pressures.  A more detailed representation of blood pressures is shown in a blood pressure profile, which graphs the blood pressure throughout the length of the different vessel groups (Figure 3).  Multiple pressure fluctuations are shown within a vessel because the pressure is traced across multiple cardiac cycles.
Figure 3  Blood pressure profile of the different vessels
Which group of blood vessels is the main source of peripheral resistance?

A)The arteries, because they cause the greatest pressure fluctuations
B)The arterioles, because they experience the largest pressure drop
C)The capillaries, because they have the smallest vessel radii
D)The venules, because they decrease blood pressure to its minimum

Question 75

Passage
Positron emission tomography (PET) is a medical imaging technique used for the detection of tumors and the evaluation of neurological functions.  A radiopharmaceutical (radioactive tracer) injected into a patient undergoes positive beta decay and emits a positron.  The positron undergoes an annihilation event with a nearby electron (<1 mm away), which emits a pair of 511 keV gamma ray photons traveling in opposite directions.  The gamma rays are detected by a ring of scintillation detectors surrounding the patient, as shown in Figure 1.  The difference in detection time between the two gamma rays from the same annihilation event is used to determine its location.  An image is constructed from data collected from multiple emission events.
Figure 1  Basic setup and process of positron emission tomographyScintillation, the emission of detectable light when excited electrons return to their ground state, occurs in crystals within the detectors due to the transfer of energy from the high energy gamma rays.  The wavelength of the emitted light depends exclusively on the type of scintillation material used (Table 1).Table 1  Common PET Scintillating Crystal Materials
The electrons in the scintillating crystals are excited through Compton scattering, a process in which a gamma ray photon acts as a particle, and transfers energy to an electron via collision.  Subsequently, the photon scatters (travels in a new direction) and its wavelength changes.  The percent change in the wavelength of the photon due to the energy loss is
Equation 1where θ is the angle between the scattered photon and electron.  Equation 1 is represented in Figure 2.
Figure 2  Percent change in photon wavelength due to Compton scattering

If one gamma photon out of a pair is Compton-scattered within the patient (not at the detector) and both gamma photons are still detected, which of the following would be seen?The frequency of the scattered photon would be lower.The point of origin would appear to be at a different location.The velocity of the photon would decrease.

A)II only
B)III only
C)I and II only
D)I and III only

Question 76

Passage
Ultrasound is a technique that uses the propagation properties of high-frequency sound waves to construct images of internal organs or to measure blood flow velocity.  The shape and position of internal organs are resolved by measuring the return time of reflected ultrasound waves.  Similarly, blood flow velocity is resolved by measuring the Doppler shift of reflected ultrasound waves.  An ultrasound device consists of an array of piezoelectric crystals and an acoustic lens.  The piezoelectric crystals generate sound when an alternating voltage is applied, and the acoustic lens increases the transmission efficiency from the device to the body by reducing sound reflection at the skin.Ultrasound is performed using frequencies in the range of 2-15 MHz.  The lower ultrasound frequencies are used for deep abdomen and obstetric/gynecological imaging due to their greater penetrating ability.  The higher ultrasound frequencies have less penetrating ability but provide higher resolution, and therefore are used for blood flow measurements and the imaging of more superficial structures.  Detailed ultrasound penetration data is shown in Figure 1.
Figure 1  Penetration in soft tissue for three different ultrasound frequenciesSound waves propagate through soft tissue at an average speed of 1,500 m/s and through blood at 1,570 m/s.
What is the period of an ultrasound signal that is attenuated by 20 dB after it travels 4 cm into soft tissue?

A)5 × 10⁻⁹ s
B)2 × 10⁻⁷ s
C)5 × 10⁻⁶ s
D)2 × 10⁻⁴ s

Question 77

Passage
Ultrasound is a technique that uses the propagation properties of high-frequency sound waves to construct images of internal organs or to measure blood flow velocity.  The shape and position of internal organs are resolved by measuring the return time of reflected ultrasound waves.  Similarly, blood flow velocity is resolved by measuring the Doppler shift of reflected ultrasound waves.  An ultrasound device consists of an array of piezoelectric crystals and an acoustic lens.  The piezoelectric crystals generate sound when an alternating voltage is applied, and the acoustic lens increases the transmission efficiency from the device to the body by reducing sound reflection at the skin.Ultrasound is performed using frequencies in the range of 2-15 MHz.  The lower ultrasound frequencies are used for deep abdomen and obstetric/gynecological imaging due to their greater penetrating ability.  The higher ultrasound frequencies have less penetrating ability but provide higher resolution, and therefore are used for blood flow measurements and the imaging of more superficial structures.  Detailed ultrasound penetration data is shown in Figure 1.
Figure 1  Penetration in soft tissue for three different ultrasound frequenciesSound waves propagate through soft tissue at an average speed of 1,500 m/s and through blood at 1,570 m/s.
Which of the following is NOT a property of sound?

A)It attenuates most in soft materials.
B)It is fastest in a vacuum.
C)It is a longitudinal wave.
D)It is a pressure wave.

Question 78

Passage
Positron emission tomography (PET) is a medical imaging technique used for the detection of tumors and the evaluation of neurological functions.  A radiopharmaceutical (radioactive tracer) injected into a patient undergoes positive beta decay and emits a positron.  The positron undergoes an annihilation event with a nearby electron (<1 mm away), which emits a pair of 511 keV gamma ray photons traveling in opposite directions.  The gamma rays are detected by a ring of scintillation detectors surrounding the patient, as shown in Figure 1.  The difference in detection time between the two gamma rays from the same annihilation event is used to determine its location.  An image is constructed from data collected from multiple emission events.
Figure 1  Basic setup and process of positron emission tomographyScintillation, the emission of detectable light when excited electrons return to their ground state, occurs in crystals within the detectors due to the transfer of energy from the high energy gamma rays.  The wavelength of the emitted light depends exclusively on the type of scintillation material used (Table 1).Table 1  Common PET Scintillating Crystal Materials
The electrons in the scintillating crystals are excited through Compton scattering, a process in which a gamma ray photon acts as a particle, and transfers energy to an electron via collision.  Subsequently, the photon scatters (travels in a new direction) and its wavelength changes.  The percent change in the wavelength of the photon due to the energy loss is
Equation 1where θ is the angle between the scattered photon and electron.  Equation 1 is represented in Figure 2.
Figure 2  Percent change in photon wavelength due to Compton scattering

The radiopharmaceutical administered to a patient is carefully chosen to provide a specific number of positron emissions per second.  If the rate of positron emissions is increased, which of the following can be expected?

A)Higher individual gamma ray energy
B)Higher gamma ray intensity
C)Higher scintillation photon frequency
D)Higher scintillation photon velocity

Question 79

Passage
Ultrasound is a technique that uses the propagation properties of high-frequency sound waves to construct images of internal organs or to measure blood flow velocity.  The shape and position of internal organs are resolved by measuring the return time of reflected ultrasound waves.  Similarly, blood flow velocity is resolved by measuring the Doppler shift of reflected ultrasound waves.  An ultrasound device consists of an array of piezoelectric crystals and an acoustic lens.  The piezoelectric crystals generate sound when an alternating voltage is applied, and the acoustic lens increases the transmission efficiency from the device to the body by reducing sound reflection at the skin.Ultrasound is performed using frequencies in the range of 2-15 MHz.  The lower ultrasound frequencies are used for deep abdomen and obstetric/gynecological imaging due to their greater penetrating ability.  The higher ultrasound frequencies have less penetrating ability but provide higher resolution, and therefore are used for blood flow measurements and the imaging of more superficial structures.  Detailed ultrasound penetration data is shown in Figure 1.
Figure 1  Penetration in soft tissue for three different ultrasound frequenciesSound waves propagate through soft tissue at an average speed of 1,500 m/s and through blood at 1,570 m/s.
Laser Doppler flowmetry uses an infrared laser to measure blood flow velocity.  Compared to ultrasound, the observed frequency shift using this technique is:

A)smaller.
B)the same.
C)larger.
D)zero.

Question 80

Passage
Ultrasound is a technique that uses the propagation properties of high-frequency sound waves to construct images of internal organs or to measure blood flow velocity.  The shape and position of internal organs are resolved by measuring the return time of reflected ultrasound waves.  Similarly, blood flow velocity is resolved by measuring the Doppler shift of reflected ultrasound waves.  An ultrasound device consists of an array of piezoelectric crystals and an acoustic lens.  The piezoelectric crystals generate sound when an alternating voltage is applied, and the acoustic lens increases the transmission efficiency from the device to the body by reducing sound reflection at the skin.Ultrasound is performed using frequencies in the range of 2-15 MHz.  The lower ultrasound frequencies are used for deep abdomen and obstetric/gynecological imaging due to their greater penetrating ability.  The higher ultrasound frequencies have less penetrating ability but provide higher resolution, and therefore are used for blood flow measurements and the imaging of more superficial structures.  Detailed ultrasound penetration data is shown in Figure 1.
Figure 1  Penetration in soft tissue for three different ultrasound frequenciesSound waves propagate through soft tissue at an average speed of 1,500 m/s and through blood at 1,570 m/s.
Blood flows toward and later passes by a doppler ultrasound probe that is fixed in place.  Relative to the probe, the velocity of blood changes from negative to positive.  Which of the following best illustrates the relationship between blood velocity v_B and the frequency shift of returning waveforms Δf?

A)
B)
C)
D)