Deck 17: Electric Forces and Fields

Question 1

About how many electrons are in 0.3 gram of water (H₂O)?

A) 10²³
B) 10²¹
C) 10²⁵
D) 10¹⁹

Answer 1

10²³

Question 2

Object A has a charge q on it, object B has a charge q on it, and object C has a charge 2q on it. These charges are arranged, one each, at the vertices of an equilateral triangle. Which charge has the greatest magnitude electric force on it?

A) A
B) C
C) B
D) All have equal magnitude forces on them.

Answer 2

C

Question 3

Two identical iron spheres have equal positive charges and the force between them when they are 1 m apart is 4 N. What percentage of the electrons has been removed from each sphere if each sphere has 1 mole (6 *10²³) of iron atoms? (k_e = 8.99 * 10⁹ N.m²/C², the atomic number of iron is 26, and the electron charge is -1.6 *10 ^{- 19} C)

A) 8 *10 ^{- 10} %
B) 0.000002%
C) 0.001%
D) 4 *10 ^{- 10} %

Answer 3

8 *10 ^{- 10} %

Question 4

Two point charges, separated by 15 cm, have charge values of +2.0 µC and -4.0 µC, respectively. What is the value of the mutual force between them? (k_e = 8.99 * 10⁹ N.m²/C²)

A) 8.0 *10 ^{- 12} N
B) 3.6 * 10 ^{- 8} N
C) 320 N
D) 3.2 N

Question 5

The constant k_e, which appears in Coulomb's law formula, is equivalent dimensionally to which of the following?

A) N/C
B) N.m²/C²
C) N/C²
D) N.m/C

Question 6

Two identical balls have the same amount of charge, but the charge on ball A is positive and the charge on ball B is negative. The balls are placed on a smooth, level, frictionless table whose top is an insulator. Which of the following is true?

A) They will move together with constant acceleration.
B) Since the force on A is equal but opposite to the force on B, they will not move.
C) Since the force on both balls is negative, they will move in the negative direction.
D) None of the above is correct.

Question 7

If the size of the charge value is tripled for one of two point charges maintained at a constant separation, the mutual force between them will be changed by what factor?

A) 3.0
B) 1/9
C) 9.0
D) 0.33

Question 8

If the distance between two point charges is quadrupled, the mutual force between them will be changed by what factor?

A) 8
B) 4
C) 1/16
D) 1/4

Question 9

Two identical spheres each carry a charge of -40.0 µC. The spheres are separated by a distance of 2.00 m. What is the electric force between the spheres? (k_e = 8.99*10⁹ N·m²/C²)

A) 43.2 N (attractive)
B) 14.4 N (repulsive)
C) 3.60 N (repulsive)
D) 7.19 N (attractive)

Question 10

A repelling force must occur between two charged objects under which conditions?

A) Charges are of equal magnitude.
B) Charges are of unlike signs.
C) Charges are of unequal magnitude.
D) Charges are of like signs.

Question 11

Doug rubs a piece of fur on a hard rubber rod, giving the rod a negative charge. What happens?

A) Protons are removed from the rod.
B) The fur is left neutral.
C) Electrons are added to the rod.
D) The fur is also charged negatively.

Question 12

Two electrons are separated by one cm. What is the ratio of the electric force to the gravitational force between them? (m_e = 9.11*10 ^{- 31} kg, k_e = 8.99 * 10⁹ N.m²/C², G = 6.67 * 10^-11 N.m²/kg², and e = 1.6 *10 ^{- 19} C)

A) 1.3 *10²⁰
B) 4.2 *10⁴²
C) 2.3 *10²
D) 3.1 * 10²²

Question 13

The charge per unit length on an insulator is . On a 2.0-m length of this material, what is the difference in the number of electrons and the number of protons?

A) There are more electrons than protons.
B) There are more protons than electrons.
C) There are more protons than electrons.
D) There are more electrons than protons.

Question 14

Two point charges are 4 cm apart. They are moved to a new separation of 8 cm. By what factor does the resulting mutual force between them change?

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

Question 15

A 6.00- $\mu$ C charge is placed at the origin and a second charge is placed on the x axis at x = 0.300 m. If the resulting force on the second charge is 6.40 N in the negative x direction, what is the force on the charge at the origin?

A) 6.40 N in the negative x direction
B) 0 N
C) 6.40 N in the positive x direction
D) not able to be determined until the second charge is known

Question 16

A 6.0-mC charge is placed at the origin and a second charge is placed on the x axis at x = 0.30 m. If the resulting force on the second charge is 5.4 N in the positive x direction, what is the value of its charge?

A) 9.0 nC
B) -9.0 nC
C) 9.0 $\degree$ C
D) -9.0 $\degree$ C

Question 17

An electron is sent at high speed toward a gold nucleus (charge +79e). What is the electrical force acting on the electron when it is 3.0*10 ^{- 13} m away from the gold nucleus? (e = 1.6 *10 ^{- 19} C, k_e = 8.99 * 10⁹ N·m²/C²)

A) 2.1 *10 ^{- 6} N
B) 2.0 * 10 ^{- 4} N
C) 0.20 N
D) 20 N

Question 18

A metallic object holds a charge of -2.9 *10^-5 C. What total number of electrons does this represent? (e = 1.6 *10^-19 C is the magnitude of the electronic charge.)

A) 1.8 *10¹⁴
B) 2.4 * 10¹³
C) 6.1 * 10¹³
D) 4.2 * 10¹⁴

Question 19

Two equal charges, each Q, are separated by some distance. What third charge would need to be placed half way between the two charges so that the net force on each charge would be zero?

A) "-Q/8"
B) "-Q"
C) "-Q/4"
D) "-Q/2"

Question 20

In a thundercloud there may be an electric charge of +40 C near the top of the cloud and -40 C near the bottom of the cloud. These charges are separated by about 2.0 km. What is the electric force between these two sets of charges? (k_e = 8.99 * 10⁹ N·m²/C²)

A) 3.6 * 10⁶ N
B) 3.6 * 10⁴ N
C) 3.6 * 10⁷ N
D) 3.6 * 10⁵ N

Question 21

Charges of 4.0 µC and -6.0 µC are placed at two corners of an equilateral triangle with sides of 0.20 m. At the third corner, what is the electric field magnitude created by these two charges? (k_e = 8.99 *10⁹ N·m²/C²)

A) 3.1 * 10⁶ N/C
B) 1.2 * 10⁶ N/C
C) 4.8 * 10⁶ N/C
D) 4.5 *10⁶ N/C

Question 22

A charge of +2 C is at the origin. When charge Q is placed at 2 m along the positive x axis, the electric field at 2 m along the negative x axis becomes zero. What is the value of Q?

A) "-7 C"
B) "-3 C"
C) "-8 C"
D) "-6 C"

Question 23

The beam of electrons that hits the screen of an oscilloscope is moved up and down by:

A) varying the electron's charge.
B) electrical charges on deflecting plates above and below the beam.
C) gravity.
D) a phosphorescent coating.

Question 24

Three equal positive charges are placed on the x-axis, one at the origin, one at x = 2 m, and the third at x = 4 m. Of the following points, which has the greatest magnitude electric field?

A) x = 1 m
B) x = 3 m
C) x = 5 m
D) The electric field has the same magnitude at all three positions.

Question 25

Charges q, q, and -q are placed on the x axis at x = 0, x = 2 m, and x = 4 m, respectively. At which of the following points does the electric field have the greatest magnitude?

A) x = 3 m
B) x = 1 m
C) x = 5 m
D) The electric field has the same magnitude at all three positions.

Question 26

Two point charges, one and the other , form a dipole separated by a distance 2L. A third charge Q is placed midway between these two charges. If the only charge that is negative is , what is the force on Q?

A) toward the
B) toward the q
C) toward the
D) toward the q

Question 27

If two 1.0-C charges have a force between them of 1.0 N, what is their separation?

A)
B) 1.0 m
C)
D)

Question 28

Two point charges are placed along a horizontal axis with the following values and positions: +3.0 µC at x = 0 cm and -6.0 µC at x = 20 cm. At what point along the x axis is the electric field zero?

A) "8.0 cm"
B) "-048 cm"
C) "-38 cm"
D) "-69 cm"

Question 29

In x-ray machines, electrons are subjected to electric fields as great as 4.0 * 10⁵ N/C. Find an electron's acceleration in this field. (m_e = 9.11 *10^-31 kg, e = 1.6 *10^-19 C)

A) 1.1 *10¹⁷ m/s²
B) 7.0 * 10¹⁶ m/s²
C) 3.6 *10⁸ m/s²
D) 4.6 * 10¹⁰ m/s²

Question 30

Electrons in a particle beam each have a kinetic energy of 3.2 *10 ^{- 17} J. What is the magnitude of the electric field that will stop these electrons in a distance of 0.05 m? (e = 1.6 * 10 ^{- 19} C)

A) 2000 N/C
B) 4000 N/C
C) 200 N/C
D) 1000 N/C

Question 31

Two charges, +Q and -Q, are located two meters apart and there is a point along the line that is equidistant from the two charges as indicated. Which vector best represents the direction of the electric field at that point?

A) Vector E_C
B) The electric field at that point is zero.
C) Vector E_B
D) Vector E_A

Question 32

Electric field is dimensionally equivalent to which of the following?

A) N/C²
B) N.m/C
C) N.m²/C²
D) N/C

Question 33

Two point charges each have a value of 30.0 mC and are separated by a distance of 3.00 cm. What is the electric field midway between the two charges? (k_e = 8.99 * 10⁹ N·m²/C²)

A) 40.5 * 10⁷ N/C
B) 20.3 *10⁷ N/C
C) zero
D) 10.1 * 10⁷ N/C

Question 34

Two point charges are separated by 10.0 cm and have charges of +1.00 µC and -1.00 µC, respectively. What is the electric field at a point midway between the two charges? (k_e = 8.99 *10⁹ N·m²/C²)

A) 14.4 *10⁶ N/C
B) zero
C) 28.8 * 10⁶ N/C
D) 7.19 *10⁶ N/C

Question 35

A proton initially moves left to right long the x axis at a speed of 2.00 * 10³ m/s. It moves into an electric field, which points in the negative x direction, and travels a distance of 0.300 m before coming to rest. If the proton's mass and charge are 1.67 *10 ^{- 27} kg and 1.60 *10 ^{- 19} C, respectively, what is the magnitude of the electric field?

A) 13.9 N/C
B) 0.0696 N/C
C) 28.3 N/C
D) 0.104 N/C

Question 36

An electron with a charge value of 1.6 *10 ^{- 19} C is moving in the presence of an electric field of 300 N/C. What force does the electron experience?

A) 2.3*10 ^{- 22} N
B) 4.8 *10 ^{- 17} N
C) 6.4 *10 ^{- 17} N
D) 1.9 *10 ^{- 21} N

Question 37

The average distance of the electron from the proton in the hydrogen atom is 0.51*10^-10 m. What is the electric field from the proton's charge at the location of the electron? (k_e = 8.99 * 10⁹ N.m²/C², e = 1.6 *10^-19 C)

A) 8.8 *10^-8 N/C
B) 1.0 * 10⁶ N/C
C) 3.2 * 10² N/C
D) 5.5 *10¹¹ N/C

Question 38

A proton moving at 6.0 * 10⁴ m/s is projected at an angle of 30 $\degree$ above a horizontal plane. If an electric field of 400 N/C is acting down, how long does it take the proton to return to the horizontal plane? (Hint: Ignore gravity. m_proton = 1.67 *10 ^{- 27} kg, q_proton = 1.6 *10 ^{- 19} C)

A) 7.8 *10 ^{- 6} s
B) 1.6 *10 ^{- 6} s
C) 7.8*10 ^{- 7} s
D) 3.9 *10 ^{- 6} s

Question 39

A proton initially moves left to right long the x axis at a speed of 2.00 *10⁴ m/s. It moves into an electric field, which points in the negative x direction, and travels a distance of 0.200 m before coming to rest. What acceleration magnitude does the proton experience?

A) 2.67 * 10¹² m/s²
B) 9.33 * 10⁹ m/s²
C) 6.67 * 10⁶ m/s²
D) 1.00 * 10⁹ m/s²

Question 40

An electron with a speed of 2.0 *10⁶ m/s moves into a uniform electric field of 325 N/C that is parallel to the electron's motion. How long does it take to bring the electron to rest? (m_e = 9.11 *10 ^{- 31} kg, e = 1.6 *10 ^{- 19} C)

A) 3.5 *10 ^{- 8} s
B) 2.3 *10 ^{- 6} s
C) 2.3 *10 ^{- 8} s
D) 1.2 * 10 ^{- 7} s

Question 41

When charging two objects by rubbing them together:

A) neither may be a conductor.
B) the heat produced by friction is a necessary part of this process.
C) they must be made of different material.
D) they will sometimes end up with both being positively charged.

Question 42

The combination of two separated point charges of opposite sign but equal magnitude is called an electric:

A) magnapole.
B) dipole.
C) quadrapole.
D) monopole.

Question 43

Two point charges, separated by 1.5 cm, have charge values of +2.0 and -4.0 µC, respectively. Suppose we determine that 10 field lines radiate out from the +2.0-µC charge. If so, what might be inferred about the -4.0 $\mu$ C charge with respect to field lines?

A) 40 radiate in
B) 20 radiate out
C) 5 radiate out
D) 20 radiate in

Question 44

Of the following substances, which one contains the highest density of free electrons?

A) glass
B) hard rubber
C) iron
D) amber

Question 45

If body M, with a positive charge, is used to charge body N by induction, what will be the nature of the charge left on the latter?

A) must be positive
B) must be equal in magnitude to that on M
C) must be negative
D) must be greater in magnitude than that on M

Question 46

If body P, with a positive charge, is placed in contact with body Q (initially uncharged), what will be the nature of the charge left on Q?

A) must be greater in magnitude than that on P
B) must be equal in magnitude to that on P
C) must be negative
D) must be positive

Question 47

Q₁ has 27 electric field lines radiating outward and Q₂ has 11 field lines converging inward. What is the ratio Q₁/Q₂?

A) "27/11"
B) ""
C) "-11/27"
D) "-27/11"

Question 48

Two small objects are suspended from threads. When the objects are moved close together, they attract one another. Which of the following could produce this result?

A) One object is negatively charged and the other is uncharged.
B) One object is positively charged and the other is uncharged.
C) One object is positively charged and the other is negatively charge.
D) All of the above could result in such attraction.

Question 49

Charge A has 10 electric field lines coming out, charge B has 20 lines coming out, and charge C has 30 lines coming in. Which pair of these charges will have the largest force between them if placed one cm apart?

A) A and B
B) B and C
C) More information is needed.
D) C and A

Question 50

A ring of charge of radius lies in the x-y plane with its center at the origin.The charge counterclockwise from is uniformly distributed with the total charge equaling Q. The charge counterclockwise from is uniformly distributed with the total charge for this half of the ring equaling . What is the direction of the electric field on the z-axis at the position ?

A) It is in the direction.
B) It is in the direction.
C) It is in the direction.
D) It has no direction since there.

Question 51

When a glass rod is rubbed with silk, which of the following statements best describes what happens?

A) Electrons are removed from the rod.
B) Protons are removed from the silk.
C) The silk remains neutral.
D) The silk is charged positively.

Question 52

The electric field in a cathode ray tube is supposed to accelerate electrons from 0 to 1.60 * 10⁷ m/s in a distance of 4.00 cm. What electric field is required? (m_e = 9.11 * 10 ^{- 31} kg and e = 1.60 *10 ^{- 19} C)

A) 18,200 N/C
B) 9110 N/C
C) 36,400 N/C
D) 72,800 N/C

Question 53

I wish to use a positively charged rod to charge a ball by induction. Which statement is correct?

A) The ball is charged as the area of contact between the two increases.
B) The ball must be a conductor.
C) The ball must be an insulator that is connected temporarily to the ground.
D) The charge on the ball will be positive.

Question 54

Five equal negative charges are uniformly spaced in a semicircular arc of radius with its center at the origin. The charges positions in polar coordinates are given by , where the values of are . At the position in the 4th quadrant, which statement best describes the direction of the resulting electric field?

A) The direction is that of a 4th quadrant angle.
B) The direction is that of a 3rd quadrant angle.
C) The direction is that of a 1st quadrant angle.
D) The direction is that of a 2nd quadrant angle.

Question 55

A ping-pong ball covered with a conducting graphite coating has a mass of 2.5 * 10 ^{- 3} kg and a charge of 4.0 µC. What electric field directed upward will exactly balance the weight of the ball? (g = 9.8 m/s²)

A) 6.1 * 10³ N/C
B) 2.0 *10 ^{- 7} N/C
C) 5.1 * 10⁶ N/C
D) 1.2 *10⁴ N/C

Question 56

Which of the following best characterizes electrical insulators?

A) high tensile strength
B) charges on the surface don't move
C) good heat conductors
D) electric charges move freely

Question 57

The electric field of a point charge has an inverse _____ behavior.

A) r³
B) r²
C) r
D) r^1/2

Question 58

An uncharged conductor is supported by an insulating stand. I pass a positively charged rod near the left end of the conductor, but do not touch it. The right end of the conductor will be:

A) neutral.
B) positive.
C) attracted.
D) negative.

Question 59

Which of the following best characterizes electrical conductors?

A) high tensile strength
B) poor heat conductors
C) electric charges move freely
D) low mass density

Question 60

The number of electric field lines passing through a unit cross sectional area is indicative of:

A) field strength.
B) charge motion.
C) field direction.
D) charge density.

Question 61

The electric field at the surface of a positively charged conductor has a direction characterized by which of the following?

A) perpendicular outward and away from the charge
B) at a 45 $\degree$ angle to the surface
C) tangent to the surface
D) perpendicular inward toward the charge

Question 62

A spherical surface surrounds a point charge at its center. If the charge is quadrupled and if the radius of the surface is doubled, what happens to the electric flux $\varPhi$ _E out of the surface and the magnitude E of the electric field at the surface as a result of these doublings?

A) " $\varPhi$ _E and E do not change."
B) " $\varPhi$ _E increases and E increases."
C) " $\varPhi$ _E increases and E remains the same."
D) " $\varPhi$ _E increases and E decreases."

Question 63

If a negative charge is placed inside a hollow isolated conductor that is originally neutral and the charge does not touch that conductor at any time:

A) both the inner and outer surfaces will become negative.
B) both the inner and outer surfaces will remain neutral.
C) the outside surface of the conductor will become positively charged.
D) the inside surface of the conductor will become positively charged.

Question 64

A charge, +Q, is placed inside a balloon and the balloon is inflated. As the radius of the balloon r increases the number of field lines going through the surface of the balloon:

A) increases proportional to r².
B) increases proportional to r.
C) stays the same.
D) decreases as 1/r.

Question 65

A charge Q accumulates on the hollow metallic dome, of radius R, of a Van de Graaff generator. A probe measures the electric field strength at various points outside the sphere surface. If the probe is initially at a distance 3R from the sphere's center and then is moved to 5R, by what factor will the electric field reading change?

A) 3/5
B) (5/3)²
C) 5/3
D) (3/5)²

Question 66

A charge Q accumulates on the hollow metallic dome, of radius R, of a Van de Graaff generator. A probe measures the electric field strength at various points outside the sphere's surface. By what factor will the electric field value at the 2R distance be changed if the charge value were increased to (5/3)Q?

A) 3/5
B) (5/3)²
C) 5/3
D) (3/5)²

Question 67

An initially uncharged hollow metallic sphere with radius of 5 cm has a small object with a charge of -10 µC carefully placed at the center of the sphere through a hole in the latter's surface. With the charge in place, what charge is now present on the outside surface of the sphere?

A) "zero"
B) "- µC"
C) "+4000 µC"
D) "+10 µC"

Question 68

We have an initially uncharged hollow metallic sphere with radius of 5.0 cm. I place a small object with a charge of +40 µC at the center of the sphere through a hole in the surface. Find the electric field present at a point 10 cm from the sphere's center. (k_e = 8.99 *10⁹ N.m²/C²)

A) 9.0 *10⁶ N/C
B) 1.1 *10⁶ N/C
C) 2.3 *10⁶ N/C
D) 36 *10⁶ N/C

Question 69

We have a hollow metallic sphere with charge +5.0 µC and radius 5.0 cm. We insert a - µC charge at the center of the sphere through a hole in the surface. What charge now rests on the outer surface of the sphere?

A) "+10 µC"
B) "+5 µC"
C) "-5 µC"
D) "+15 µC"

Question 70

How can a charged object attract an uncharged object made of non-conducting material?

A) The charges in the uncharged object can become polarized.
B) The uncharged object must somehow gain a like charge.
C) Attraction of an insulator is not possible.
D) The uncharged object must somehow gain an unlike charge.

Question 71

A conducting spherical shell of inner radius and outer radius has a charge Q on it. An additional charge, also Q, is then added to the sphere. What is the resulting charge per unit area on the outer surface of the sphere?

A)
B) No answer given is correct.
C)
D)

Question 72

A conducting spherical shell of inner radius and outer radius has a charge Q on it. The flux through a concentric spherical surface of radius is . An additional charge, also Q, is then added to the sphere. What is the change in flux through a concentric spherical surface of radius when the additional charge is placed on the conducting shell?

A)
B)
C)
D) 0

Question 73

In an electrophoresis experiment, the terminal speed of a particular DNA fragment is v_T . If the experiment is repeated with identical fragments with the voltage between the plates producing the field increased by 50%, what new terminal speed would occur? Choose the closest answer.

A) 1.6 v_T
B) 1.5 v_T.
C) 2.3 v_T
D) 0.50 v_T

Question 74

An initially uncharged hollow metallic sphere with radius of 5 cm has a small object with a charge of -10 µC carefully placed at the center of the sphere through a hole in the latter's surface. What charge resides inner surface of the sphere?

A) "- µC"
B) "zero"
C) "+10 µC"
D) "-4000 µC"

Question 75

The electric field associated with a uniformly charged hollow metallic sphere is the greatest at:

A) the center of the sphere.
B) the sphere's outer surface.
C) infinity.
D) the sphere's inner surface.

Question 76

A proton consists of 3 quarks, two with charge +2e/3 and one with charge -e/3. Of the following, which is closest to the approximate potential energy of the arrangement of the two positive quarks if they are separated by 10^-15 m?

A) 1 MeV
B) 10^-19 MeV
C) 10¹² MeV
D) 100 MeV

Question 77

A Van de Graaff generator has a spherical dome of radius 12 cm. Operating in dry air, where "atmospheric breakdown" is at E_max = 3.0 *10⁶ N/C, what is the maximum charge that can be held on the dome? (k_e = 8.99 *10⁹ N.m²/C²)

A) 4.8 * 10^-6 C
B) 1.3 * 10^-5 C
C) 2.7 * 10^-5 C
D) 3.3 *10^-6 C

Question 78

If a conductor is in electrostatic equilibrium near an electrical charge:

A) the sum of all forces between the conductor and the charge must be zero.
B) the total charge on the conductor must be zero.
C) any charges on the conductor must be uniformly distributed.
D) the electric field inside the conductor must be zero.

Question 79

A thin uncharged conducting spherical shell has a charge q carefully placed at its center through a small hole in the shell. The charge q does not touch the shell. What is the charge on the shell?

A) "2q"
B) "0"
C) "q"
D) "-q"

Question 80

A spherical volume of space has an electric field of intensity 170 N/C directed radially outward from it surface of radius 0.600 m. What is the net charge enclosed within this surface?

A) -6.8 nC
B) -4.0 nC
C) 4.0 nC
D) 6.8 nC