Deck 29: Electromagnetic Induction

Question 1

An emf of 10 V is applied to a coil having a resistance of 0.50 $\varOmega$ .If it takes 0.55 s for the current to reach one half of its maximum value,what is the inductance of the coil?

A)229 mH
B)312 mH
C)397 mH
D)40 mH

Answer 1

397 mH

Question 2

An emf of 10 V is applied to a coil having an inductance of 40 mH resistance of .If it takes 0.55 s for the current to reach one half of its maximum value,what is the resistance of the coil?

A)0.050 $\varOmega$
B)0.50 $\varOmega$
C)0.11 $\varOmega$
D)0.037 $\varOmega$

Answer 2

0.050 $\varOmega$

Question 3

Solenoid two is twice as long and has twice as many turns of wire as solenoid one.Both solenoids have the same cross-sectional area.What is the ratio of the inductance of solenoid two to the inductance of solenoid one?

A)1
B)2
C)4
D)8

Answer 3

2

Question 4

An emf of 10 V is applied to a coil with an inductance of 40 mH and a resistance of 0.50 $\varOmega$ .Determine the energy stored in the magnetic field when the current reaches one half of its maximum value.

A)0.020 J
B)0.20 J
C)2.0 J
D)20 J
E)200 J

Question 5

An emf of 10 V is applied to a coil with an inductance of 40 mH and a resistance of 5.0 .Determine the energy stored in the magnetic field when the current reaches its maximum value.

A)0.080 J
B)0.80 J
C)8.0 J
D)80 J
E)800 J

Question 6

An inductor of inductance L and a resistor of resistance R are connected in series and then at t = 0 the combination is connected across the terminals of a battery.When is the current flowing through the resistor equal to half its maximum value?

A)t = L/2R
B)t = L/R
C)t = 2L/R
D)None are correct.

Question 7

An inductor of inductance L and a resistor of resistance R are connected in series.This series combination is then connected across the terminals of a battery.After a very long time,the battery is suddenly removed from the circuit and the circuit is made to form a closed loop so that the current continues to flow.How long after the battery is removed is the current flowing through the resistor equal to half its value before the battery was removed?

A)t = L/2R
B)t = L/R
C)t = 2L/R
D)None are correct.

Question 8

An emf of 10 V is applied to a coil with an inductance of 40 mH and a resistance of 0.50 $\varOmega$ .How long does it take for the current to reach one half of its maximum value?

A)0.055 s
B)0.55 s
C)5.5 s
D)55 s

Question 9

A loop of wire lies motionless on a flat,horizontal surface in the presence of a uniform and constant magnetic field.When is the magnetic flux through the area interior to the loop the largest?

A)when the magnetic field is parallel to the area interior to the loop
B)when the magnetic field is perpendicular to the area interior to the loop
C)when the magnetic field is only exists exterior to the loop
D)None are correct.

Question 10

A solenoid with 100 turns and a cross sectional area of 20 cm² has a magnetic field of 0.60 T along its axis.If the field is confined within the solenoid and changes at a rate of 0.20 T/s,the magnitude of the induced EMF in the solenoid will be

A)0.0080 V.
B)0.080 V.
C)0.040 V.
D)0.40 V.

Question 11

Which of the following will not produce an induced potential difference in a loop of copper wire in the presence of a uniform and constant magnetic field?

A)The loop moves in a straight line but does not rotate.
B)The loop rotates but does not move in a straight line.
C)The loop both moves in a straight line and rotates.
D)None are correct.

Question 12

A 2.0 m long solenoid of cross sectional area 1.4 m² and n=300 turns/m carries a current of 4.0 A.What is the energy density in the solenoid?

A)0.95 J/m³
B)0.90 J/m³
C)1.1 J/m³
D)0.81 J/m³

Question 13

A 5-turn square loop (0.150 m along a side,resistance = 2.00 $\varOmega$ )is placed in a magnetic field that makes an angle of 30 ^$\circ$ with the normal to the plane of the loop.The magnitude of this field varies with time according to B = 2.40t⁴,where t is measured in s and B in T.What is the induced current in the coil at t = 1.25 s?

A)1.47 A
B)1.23 A
C)0.913 A
D)0.527 A
E)0.351 A

Question 14

A 5-turn square loop (0.150 m along a side,resistance = 2.00 $\varOmega$ )is placed in a magnetic field that makes an angle of 30 ^$\circ$ with the normal to the plane of the loop.The magnitude of this field varies with time according to B = 2.40t⁴,where t is measured in s and B in T.What is the induced EMF in the coil at t = 1.38 s?

A)2.67 V
B)2.87 V
C)1.45 V
D)2.03 V
E)2.46 V

Question 15

A 10-turn square loop (0.250 m along a side,resistance = 4.00 $\varOmega$ )is placed in a magnetic field that makes an angle $\alpha$ with the normal to the plane of the loop.The magnitude of this field varies with time according to B = 2.70t²,where t is measured in s and B in T.The induced current in the coil at t = 1.50 s is 0.750 A. The angle $\alpha$ made by the magnetic field with the plane of the loop is

A)30.0 ^$\circ$ .
B)60.0 ^$\circ$ .
C)36.3 ^$\circ$ .
D)53.7 ^$\circ$ .

Question 16

A solenoid of cross sectional area 1.4 m² and n=300 turns/m carries a current of 4.0 A.It stores an energy of 3.4 J.What is the length of the solenoid?

A)3.5 m
B)2.3 m
C)2.0 m
D)3.1 m
E) 2.7 m

Question 17

A solenoid of cross sectional area 1.4 m² and 2.0 m long carries a current of 4.0 A.It stores an energy of 3.4 J.How many turns per unit length are in this solenoid?

A)390 turns/m
B)300 turns/m
C)450 turns/m
D)420 turns/m
E) 350 turns/m

Question 18

A 2.0 m long solenoid of cross sectional area 1.4 m² and 300 turns/m carries a current.It stores an energy of 3.4 J.What is the current in the solenoid?

A)4.3 A
B)4.0 A
C)5.2 A
D)4.9 A
E)4.6 A

Question 19

A long solenoid of length 2.0 m and n=300 turns/m carries a current of 4.0 A.It stores an energy of 3.4 J.What is the cross sectional area of the solenoid?

A)0.70 m²
B)1.2 m²
C)1.4 m²
D)1.7 m²
E) 1.9 m²

Question 20

A 2.0 m long solenoid of cross sectional area 1.4 m² and n=300 turns/m carries a current of 4.0 A.What is the energy stored in the solenoid?

A)3.4 J
B)3.1 J
C)2.5 J
D)2.2 J

Question 21

Which of the following has the largest inductance?

A)a solenoid of radius 1cm,length 5 cm,and with 100 turns of wire per centimeter
B)a solenoid of radius 3cm,length 1 cm,and with 100 turns of wire per centimeter
C)a solenoid of radius 2cm,length 2 cm,and with 100 turns of wire per centimeter
D)a solenoid of radius 1cm,length 1 cm,and with 200 turns of wire per centimeter
E)a solenoid of radius 2 cm,length 5 cm,and with 100 turns of wire per centimeter

Question 22

Electrons are circulating in a 0.58 m diameter cyclotron orbit in a uniform magnetic field of 1.1 T.One can think of these circulating electrons as a circular current loop with the same diameter.The magnetic field is then rapidly increased at a constant rate of 2.5 T/s.What is the magnitude of the induced electric field causing the electrons to increase their speed 25 ms after the magnetic field begins increasing? This is the basis for accelerating electrons in a betatron.

A)0.018 V/m
B)0.36 V/m
C)0.73 V/m
D)7.0 V/m
E)14 V/m.

Question 23

A popular demonstration of eddy currents is to drop a magnet down a long metal tube and a long glass or plastic tube.As the magnet falls down the tube there is changing flux as the magnet falls toward or away from each part of the tube.What tube has the larger voltage induced in it and what one has the larger current induced in it. V I

A)metal metal
B)glass glass
C)glass metal
D)same metal
E)same same

Question 24

A 7.2-mH inductor is connected to a current.What is the magnitude of the voltage in the inductor at time t = 3.0 s if the current is I(t)= 5 + 7t -2t²? (Assume two significant digits for each number.)

A)22 mV
B)36 mV
C)58 mV
D)90 mV
E)230 mV

Question 25

A single rectangular wire loop with a height of 24.0 cm and a width of 10.0 cm is mounted flat on an office door.The resistance of the loop is 3.85 $\varOmega$ .The Earth's magnetic field of 2.6 * 10^-5 T is uniform and perpendicular to the surface of the closed door.The door is then opened at a constant rate of 4.6 rad/s.Calculate the magnitude of the induced current 0.434 s after the door begins opening.

A)4.7 * 10^-6 A
B)4.1 * 10^-7 A
C)1.1 * 10^-7 A
D)1.3 * 10^-6 A
E)6.8 * 10^-7 A

Question 26

Electrons are circulating in a 0.58 m diameter cyclotron orbit in a uniform magnetic field of 1.1 T.One can think of these circulating electrons as a circular current loop with the same diameter.The magnetic field is then rapidly increased at a constant rate.If the magnitude of the induced electric field causing the electrons to increase their speed 25 ms after the magnetic field begins increasing is 0.73 V/m,what is rate at which the field is increasing? This is the basis for accelerating electrons in a betatron.

A)2.5 T/s
B)5.0 T/s
C)1.3 T/s
D)4.1 T/s
E)3.3 T/s

Question 27

A supersonic airplane with a wingspan of 10 m is flying over the north magnetic pole (with a magnetic field of 0.5 G perpendicular to the ground)at a speed of three times the speed of sound (Mach 3).What is the potential difference from one end of the wing to the other? Assume that the aircraft wings are made of aluminum.

A)0.25 V
B)0.5 V
C)0.75 V
D)1.0 V
E)1.25 V

Question 28

A 2.7-mH inductor is connected to a current.How much energy is stored in its magnetic field at time t = 3.0 s if the current is ? (Assume two significant digits for each number.)

A)0.0095 J
B)0.041 J
C)0.066 J
D)0.13 J
E)0.30 J

Question 29

An elastic circular conducting loop expands at a constant rate in time.The radius is initially 0.200 m,but then begins to increase 0.018 m every second.The loop has a constant resistance of 15 $\varOmega$ and is placed in a region of uniform (same everywhere)magnetic field of 0.880 T,perpendicular to the plane of the loop.Calculate the magnitude of the induced EMF 2.4 s after the loop begins expanding.

A)31.2 mV
B)24.2 mV
C)22.3 mV
D)28.0 mV
E)19.9 mV

Question 30

A metal loop has an area of 0.450 m² and is placed flat on the ground.There is a uniform magnetic field pointing directly out of the ground.This magnetic field initially has a value of 0.728 T but this decreases to 0.150 T uniformly during a period of 0.238 s.Find the voltage induced in the loop during this time.

A)zero
B)0.26 V
C)1.1 V
D)1.7 V
E)2.4 V

Question 31

A rectangular (45 cm long by 22 cm wide)circuit loop with resistance 35 $\varOmega$ is held parallel to the xy-plane with one end inside a uniform magnetic field.The magnetic field for x < 0 is 1.8 T along +z axis,and for x > 0 the magnetic field is zero.Initially the left end of the loop is at x = -30 cm and the right end is at x = 15cm.Calculate the magnitude of the force required to move the loop to the right along the positive x-axis at a constant speed of 13 cm/s while the left end of the loop is still in the magnetic field.

A)5.8 * 10^-4 N
B)3.2 * 10^-4 N
C)1.5 * 10^-3 N
D)1.6 * 10^-2 N
E)2.0 * 10^-2 N

Question 32

Electrons are circulating in a cyclotron in a uniform magnetic field of 1.1 T.One can think of these circulating electrons as a circular current loop with the same diameter.The magnetic field is then rapidly increased at a constant rate of 2.5 T/s.If the magnitude of the induced electric field causing the electrons to increase their speed 25 ms after the magnetic field begins increasing is 0.73 V/m,what is the diameter of the electrons' orbit? This is the basis for accelerating electrons in a betatron.

A)1.17 m
B)0.29 m
C)1.03 m
D)0.58 m
E)1.45 m

Question 33

What is the resistance of a series RL circuit in which L = 73 mH if the current increases to a quarter of its final value in 14 $\mu$ s?

A)1.5 k $\varOmega$
B)2.6 k $\varOmega$
C)3.2 k $\varOmega$
D)4.7 k $\varOmega$
E)5.8 k $\varOmega$

Question 34

A metal loop has an area of 0.780 m² and is placed flat on the ground.Initially there is a uniform magnetic field pointing directly out of the ground of magnitude 0.326 T.This changes uniformly to a magnetic field pointed downward of magnitude 0.114 T during a period of 0.719 s.Find the voltage induced in the loop during this time.

A)zero
B)0.23 V
C)0.25 V
D)0.48 V
E)0.62 V

Question 35

An elastic circular conducting loop expands at a constant rate in time.The radius is initially 0.200 m,but then begins to increase 0.018 m every second.The loop has a constant resistance of and is placed in a region of uniform (same everywhere)magnetic field of 0.880 T,perpendicular to the plane of the loop.Calculate the resistance of the loop if magnitude of the induced current 2.4 s after the loop begins expanding is 1.3 * 10^-3 A)

A)21.9 $\varOmega$
B)15.0 $\varOmega$
C)13.4 $\varOmega$
D)11.4 $\varOmega$
E) 18.6 $\varOmega$

Question 36

Two conducting rails of negligible resistance terminate in a resistor of resistance R = 2.40 $\varOmega$ The rails are placed in a magnetic field B = 15.0 mT perpendicular to the plane of the rails.The magnetic field is uniform and time independent.The distance between the rails is w = 10.0 cm as shown in the figure.A conducting rod of negligible resistance slides frictionless on top of the two rails at a velocity v = 1.20 m/s + (3.4 m/s²)t,where t is the time,in seconds.The induced current in the circuit at t = 1.00 s is

A)2.88 mA.
B)1.81 mA.
C)1.28 mA.
D)0.978 mA.
E)0.836 mA.

Question 37

An elastic circular conducting loop expands at a constant rate in time.The radius is initially 0.200 m,but then begins to increase 0.018 m every second.The loop has a constant resistance of 15 $\varOmega$ and is placed in a region of uniform (same everywhere)magnetic field of 0.880 T,perpendicular to the plane of the loop.Calculate the magnitude of the induced current 2.4 s after the loop begins expanding.

A)0 A
B)1.3 * 10^-3 A
C)1.6 * 10^-3 A
D)8.0 * 10^-4 A
E)2.1 * 10^-3 A

Question 38

Which of the following methods will induce a current in a loop of wire in a uniform magnetic field?

A)decreasing the strength of the field
B)rotating the loop about an axis parallel to the field
C)translating the loop about the field
D)All are correct.
E)None are correct.

Question 39

A metal loop has an area of 0.100 m² and is placed flat on the ground.There is a uniform magnetic field pointing due west.This magnetic field initially has a value of 0.123 T but this decreases to 0.075 T uniformly during a period of 0.579 s.Find the voltage induced in the loop during this time.

A)zero
B)2.8 mV
C)8.3 mV
D)11 mV
E)34 mV

Question 40

What is the inductance of a series RL circuit in which R = 2.0 k $\varOmega$ if the current increases to one third of its final value in 10 $\mu$ s?

A)87 mH
B)70 mH
C)58 mH
D)49 mH
E)36 mH

Question 41

Hyperthermia is one of the modalities for cancer treatment.In the procedure,the magnetic nanoparticles are injected at the tumor site which is then exposed to radio frequency electromagnetic waves.The radio frequency waves induce oscillations among the magnetic nanoparticles causing their temperature to rise.A modest increase in the temperature at the tumor site (about106 ^$\circ$ F)can kill cancer cells.A solenoid is one of the components used for producing the radio frequency waves.If 102 turns of copper wire are used to construct a 10-cm long and 6-cm radius solenoid,what is the indcutance of the solenoid?

A)5.00 mH
B)1.48 mH
C)9.55 mH
D)16.9 mH
E)3.89 mH

Question 42

A circular wire loop of resistance R = 1.0 $\varOmega$ rotates with period 150 ms about a horizontal axis while in a region having a 0.10 T magnetic field pointing in a horizontal plane at an angle of 35 degrees relative to the rotation axis.If the maximum current induced in the loop is 6.7 mA,what is the diameter of the loop?

A)6.0 cm
B)2.8 cm
C)5.0 cm
D)4.2 cm
E)6.5 cm

Question 43

A solenoid of radius 2 cm and length 15 cm has 120 turns.If the rate of change of induced current through it is 12.9 A/s,what is the self-induced emf?

A)2.71 mV
B)3.41 mV
C)1.96 mV
D)4.00 mV

Question 44

A conducting ring is moving from left to right through a region that contains a constant magnetic field as shown in the diagram.In which regions is there an induced current in the ring?

A)regions B and D
B)regions B,C,and D
C)region C
D)All regions have an induced current in the ring.

Question 45

The magnetic field in the coil is upward and decreasing.The direction of the induced current in the coil,as viewed from the top is

A)clockwise.
B)counterclockwise.
C)There is no induced current.

Question 46

The speed of a 15-cm long wire in a 100- mT magnetic field to produce a 3-V motional emf is

A)2 m/s.
B)25 m/s.
C)41 m/s.
D)200 m/s.

Question 47

The long straight wire in the figure has current I = 1 A flowing in it.A square loop which has 10-cm sides is positioned 10 cm away from the wire as shown.The loop is then moved in the positive x-direction with a speed v = 10 cm/s.If the loop has a resistance of 0.02 ohms,calculate the direction and the magnitude of the induced current in the loop the instant the loop is made to move.

A)0.50 $\mu$ A clockwise
B)0.50 $\mu$ A counter-clockwise
C)6.7 $\mu$ A clockwise
D)6.7 $\mu$ A counter-clockwise
E)1.3 $\mu$ A clockwise

Question 48

A washer with inner diameter 5.0 cm is carried in your pocket as you walk directly north according to your magnetic compass.Assume the normal to the washer's plane is exactly horizontal,pointing toward magnetic north.The Earth's magnetic field strength is 0.056 mT.If the magnetic flux through the washer's opening is 36 nTm²,what is the angle below local horizontal that the magnetic field vector points?

A)71 ^$\circ$
B)19 ^$\circ$
C)85 ^$\circ$
D)4.7 ^$\circ$
E)None are correct.

Question 49

A circular wire loop of diameter 5.0 cm rotates with period 150 ms about a horizontal axis while in a region having a 0.10 T magnetic field pointing in a horizontal plane at an angle of 35 degrees relative to the rotation axis.If the maximum current induced in the loop is 6.7 mA,what is the resistance of the loop?

A)0.445 $\varOmega$
B)1.13 $\varOmega$
C)0.876 $\varOmega$
D)0.704 $\varOmega$
E)1.00 $\varOmega$

Question 50

The long straight wire in the figure has current I = 1 A flowing in it.A square loop which has 10-cm sides is positioned 10 cm away from the wire as shown.The loop is then moved in the positive x-direction with a speed v = 10 cm/s.If the loop has a resistance of 0.02 ohms,calculate the direction and the magnitude of the net force acting on the loop the instant the loop is made to move.

A)3 * 10^-7 N to the right
B)2 * 10^-6 N to the left
C)7 * 10^-10 N to the right
D)5 * 10^-14 N to the left

Question 51

A solenoid of radius 2 cm and length 15 cm has 120 turns.The rate of change of induced current through it to produce a self-induced emf of 4 mV is

A)2.3 A/s.
B)8.5 A/s.
C)12.9 A/s.
D)26.3 A/s.

Question 52

The figure shows the current through an inductor.If the maximum magnitude of the potential difference $\Delta$ V_L across the inductor over the period shown is 60 V,what is the inductance of the inductor?

A)100 mH
B)1 mH
C)10 mH
D)1 H

Question 53

The long straight wire in the figure has current I = 1 A flowing in it.A square loop which has 10-cm sides is positioned 10 cm away from the wire as shown.The loop is then moved in the positive x-direction with a speed v = 10 cm/s.If the loop has a resistance of 0.02 ohms,calculate the magnitude of the magnetic flux through the loop the instant the loop is made to move.

A)1.39 * 10^-8 T-m²
B)1.48 * 10^-8 T-m²
C)1.22 * 10^-8 T-m²
D)1.33 * 10^-8 T-m²

Question 54

Hyperthermia is one of the modalities for cancer treatment.In the procedure,the magnetic nanoparticles are injected at the tumor site which is then exposed to radio frequency electromagnetic waves.The radio frequency waves induce oscillations among the magnetic nanoparticles causing their temperature to rise.A modest increase in the temperature at the tumor site (about106 ^$\circ$ F)can kill cancer cells.A solenoid is one of the components used for producing the radio frequency waves.The number of turns of copper wire needed to construct a 10-cm long,6-cm radius,and 5-mH inductance solenoid are

A)188.
B)102.
C)67.
D)42.
E)2.1.

Question 55

A circuit consists of a 1-mH inductor connected in series with a 2- $\varOmega$ resistor and a 10-V battery connected for a long time.After the battery is removed from the circuit,how long does it take the current in the circuit to drop to half of its original value?

A)2.4 ms
B)1.2 ms
C)0.73 ms
D)0.35 ms
E)0.14 ms

Question 56

The conducting loop in the shape of a quarter-circle has a radius of 10 cm and resistance of 0.2 ohms.The magnetic field strength within the dotted circle of 3-cm radius is initially 2 T.If the magnetic field strength decreases from 2 T to 1 T in 2 s,find the magnitude and the direction of the induced current in the loop.

A)1.414 A,counter-clockwise
B)7.07 mA,clockwise
C)1.414 A,clockwise
D)0.707 A,counter-clockwise

Question 57

The figure shows the current through a 10-mH inductor.What is maximum magnitude of the potential difference $\Delta$ V_L across the inductor over the period shown?

A)20 V
B)40 V
C)60 V
D)60 mV

Question 58

The magnetic field in the coil is upward and increasing.The direction of the induced current in the coil,as viewed from the top is

A)clockwise.
B)counterclockwise.
C)There is no induced current.

Question 59

A loop of wire sits in the plane of the page you are looking at,and the magnetic field in which the loop is sitting comes out of the page and is increasing in strength with time according to B = B₀t².What properly describes the current induced in the loop?

A)clockwise,getting bigger
B)clockwise,getting smaller
C)counter-clockwise,getting bigger
D)counter-clockwise,getting smaller
E)None are correct.

Question 60

A circular wire loop of resistance 1.00 $\varOmega$ and diameter 5.0 cm rotates about a horizontal axis while in a region having a 0.10 T magnetic field pointing in a horizontal plane at an angle of 35 degrees relative to the rotation axis.If the maximum current induced in the loop is 6.7 mA,what is the period of the rotation?

A)106 ms
B)164 ms
C)150 ms
D)93.2 ms
E)85.9 ms

Question 61

A circular coil of wire with 200 turns and a radius of 30 cm is laying flat on a horizontal wooden table.There is a uniform magnetic field at this location with a magnitude of 0.3 T that is directed to the north and down,making an angle of 25.8 ^$\circ$ with the horizontal.What is the magnitude of the magnetic flux through the coil?

A)3.1 Tm²
B)7.4 Tm²
C)9.4 Tm²
D)15 Tm²
E)17 Tm²

Question 62

An LR circuit is hooked up to a battery as shown in the figure,with the switch initially open.The resistance in the circuit is R = 11.0,the inductance is L = 3.00 H,and the battery maintains a voltage of E = 36.0 V.At time t = 0 the switch is closed.How much time (in seconds)does it take until the voltage across the resistor is equal to the voltage across the inductor?

A)0.189
B)0.236
C)0.295
D)0.369
E)0.462

Question 63

A 15-mH inductor is connected in series with a battery and a 12- $\varOmega$ resistor,in a circuit with an open switch.0.50 ms after the switch is closed,the current in the circuit is 1.2A. What is the EMF supplied by the battery?

A)44 V
B)21 V
C)3.6 V
D)1.8 V

Question 64

A coil is in a perpendicular magnetic field that is time dependent and given by B = 0.600 - 3.7t T.If the induced voltage around the coil is 7.4 V,what is its area in m²?

A)12.2
B)2.0
C)0.005
D)5.0 * 10^-5
E)0.600

Question 65

In the figure shown,the field is decreasing by 150 T/s.What is the magnitude of the current in amperes?

A)0.18
B)0.22
C)0.40
D)0.62
E)144

Question 66

A 1.0-m long straight wire is held in a horizontal east-west orientation and is then dropped.Supposing that the Earth's magnetic field at this location is 2.0 * 10^-5 T,due north,what will be the induced emf in the wire 2.0 s after it is released? (Hint: The wire is in free-fall,and you can thus calculate its velocity after the 2.0 s.)

A)3.9 * 10^-4 V
B)4.0 * 10^-2 V
C)4.0 * 10^-1 V
D)2.1 * 10^-1 V
E)1.2 * 10² V

Question 67

In the circuit shown,what is the time required for the current to reach 63% (= 1 - e^-1)of its final value after the switch is closed? R = 500 $\varOmega$ and L = 67 H.

A)0.134 s
B)0.440 s
C)0.632 s
D)2.520 s
E)7.463 s

Question 68

What is the peak voltage generated by a rotating rectangular 4.0 cm by 5.4 cm,68 turn coil in a magnetic field,B= 0.78 T? The coil rotates at 60 Hz.

A)3.4 V
B)110 V
C)43.2 V
D)21.3 V
E)55.4 V

Question 69

When the switch in the circuit below is closed,what will happen?

A)The current will start at I = V/R in the direction shown and then drop to zero.
B)The current will gradually rise to I = V/R in the direction shown.
C)The current will rise slowly to a final value of I = RL.
D)No current will flow.
E)The current will gradually rise to I = V/R in the direction opposite to that shown.

Question 70

A circular wire loop of resistance R = 1.0 $\varOmega$ and diameter 5.0 cm rotates with period 150 ms about a horizontal axis while in a region having a 0.142 T magnetic field pointing in a horizontal plane at an angle of 35 degrees relative to the rotation axis.At time t = 0 the plane of the loop is horizontal.What is the magnitude of the induced EMF in the loop at a time of t = 75ms?

A)4.7 mV
B)0.75 mV
C)6.7 mV
D)0
E)8.2 mV

Question 71

A long,straight wire is located along the y-axis.The wire carries a current in the +y direction that is changing as a function of time according to I = 3.0 A + (0.20 A/s)t.A loop of wire is located in the x-y plane near the loop as shown in the figure.The loop has dimensions of 7m * 5m and is 1m away from the wire.What is the induced emf in the wire loop at the time t = 4.0 s?

A)4.2 * 10^-7 V
B)8.3 * 10^-7 V
C)6.7 * 10^-6 V
D)7.9 * 10^-6 V
E)1.3 * 10^-5 V

Question 72

In the circuit shown,R = 1200 $\varOmega$ ,L = 6.0 H,and V = 9.0 V.After switch S is closed,how long will it take the current in the inductor to reach 4.0 mA?

A)2.3 ms
B)2.7 ms
C)3.8 ms
D)5.0 ms
E)7.7 ms

Question 73

The current in the wire is given by the equation I = 2.5 - 0.6t,with positive to the right as shown.Which of the statements concerning the current induced in the loop is correct?

A)There is no induced current.
B)The current is clockwise always.
C)The direction of current depends on the value of r.
D)The current is first clockwise then counterclockwise.

Question 74

How much energy is stored in a long solenoid with 660 turns,length L = 3.2 m,and a cross sectional area A = 121 cm²,when the current in it is I = 85 A?

A)1.1 mJ
B)9.11 kJ
C)1.1 kJ
D)5.21 J
E)7.48 J

Question 75

How large a current must flow through an L = 1.2 H inductance so that the energy stored is 393 J?

A)1.17 A
B)2.31 A
C)25.6 A
D)44.2 A
E)107.1 A

Question 76

A conducting rod is pulled horizontally with constant force F = 5.00 N along a set of rails separated by d = 0.56 m.A uniform magnetic field B= 0.60 T is directed into the page.There is no friction between the rod and the rails,and the rod moves with constant velocity v = 4.00 m/s.Using Faraday's Law,calculate the magnitude of the induced emf (in V)around the loop in the figure that is caused by the changing flux.

A)1.344
B)1.788
C)2.377
D)3.162
E)4.205

Question 77

An RL circuit with a resistor with R = 8.80 $\varOmega$ and an inductor with inductance L = 3.70 mH has an energy of 3.00 J with the switch in position a.At time = 0 seconds,the switch is moved to position b.What is the current (in a)after 1.90 milliseconds?

A)0.321
B)0.375
C)0.439
D)0.514
E)0.601

Question 78

A 9-V battery is connected through a switch to 2 identical resistors and an ideal inductor as shown in the figure.The 2 resistors each have a resistance of 20 ohms and the inductor has an inductance of 0.10 henries.The switch is initially open.Ten milliseconds after the switch is closed,what is the current in resistor R₂?

A)0.19 A
B)0.23 A
C)0.28 A
D)0.39 A
E)0.44 A

Question 79

A single loop of wire with an area of 0.40 m² is located in the plane of this paper as shown.There is a time-varying magnetic field at the location of the loop.It is directed into the page and its magnitude is given by B = 2T + (3T/s)t.At t = 5.0 s,what is the induced emf in the loop?

A)1.2 V
B)1.4 V
C)1.7 V
D)6.0 V
E)6.8 V

Question 80

A solenoid has N = 490 loops of wire and a cross-sectional area A = 15 cm².It is moved from a field-free region to one where the magnetic field B = 0.8 T points directly along the axis of the solenoid.If the motion proceeds with constant velocity and takes t = 15 seconds,what is the magnitude of the average induced EMF?

A)0.039 V
B)1.25 V
C)12.0 V
D)125 V
E)4900 V