Deck 28: Magnetic Induction

Question 1

A circular wire coil of radius 25 cm and 20 turns is sitting in a perpendicular magnetic field of 0.2 T.If the coil is flipped over,what is the change in magnetic flux through the loop?

A)0 Wb
B)1.6 Wb
C)0.080 Wb
D)0.80 Wb
E)0.040 Wb

Answer 1

1.6 Wb

Question 2

The magnetic flux through a loop is made to vary according to the relation where the units are SI.The EMF induced in the loop when t = 2 s is

A)38 V
B)39 V
C)40 V
D)31 V
E)19 V

Answer 2

31 V

Question 3

A circular loop of radius 25 cm is sitting in a perpendicular magnetic field of 0.2 T.If the magnetic field strength changes to a value of 0.5 T in 2.5 s,calculate the induced EMF in the loop.

A)7.5 $\times$ 10^-3 V
B)9.6 $\times$ 10^-2 V
C)4.0 $\times$ 10^-2 V
D)2.4 $\times$ 10^-2 V
E)none of the above

Answer 3

2.4 $\times$ 10^-2 V

Question 4

The plane of a circular,200-turn coil of radius 5.25 cm is perpendicular to a uniform magnetic field produced by a large electromagnet.This field is changed at a steady rate from 0.650 T to 0.150 T in 0.0100 s.What is the magnitude of the EMF induced in the coil?

A)110 V
B)170 V
C)1.7 V
D)26 V
E)87 V

Question 5

The magnetic flux through a certain coil is given by where the units are SI.The coil has 100 turns.The magnitude of the induced EMF when t = 1/200 s is

A)100 V
B)200 V
C)zero
D)2/ $\pi$ V
E)1/50 $\pi$ V

Question 6

A 3.0-cm by 5.0-cm rectangular coil has 100 turns.Its axis makes an angle of 55º with a uniform magnetic field of 0.35 T.It requires 0.33 s to turn the coil until its plane is perpendicular to the magnetic field.What is the (average)magnitude of the induced EMF?

A)0.16 V
B)0.13 V
C)91 mV
D)68 mV
E)29 mV

Question 7

Use the following figure for the next problem.

-A rectangle is bent on two sides at 90 ^$\circ$ so that one end lies along the xy plane while the other end lies along the xz plane.The length a = 10 cm and b = 30 cm.A magnetic field of strength B = 0.1 T lies in the yz plane and points at an angle $\theta$ = 30 ^$\circ$ with the y axis.The flux through the rectangle is

A)52.0 mWb
B)30.0 mWb
C)41.0 mWb
D)60.0 mWb
E)None of these is correct.

Question 8

Suppose you double the magnetic field in a given region and quadruple the area through which this magnetic field exists.The effect on the flux through this area would be to

A)leave it unchanged.
B)double it.
C)quadruple it.
D)increase it by a factor of six.
E)increase it by a factor of eight.

Question 9

A square coil of wire with side 8.0 cm and 50 turns sits in a uniform magnetic field that is perpendicular to the plane of the coil.The coil is pulled quickly out of the magnetic field in 0.2 s.If the resistance of the coil is 15 ohm and a current of 12 mA is induced in the coil,calculate the value of the magnetic field.

A)5.6 T
B)0.11 T
C)7.5 $\times$ 10^-3 T
D)1.4 T
E)9.1 T

Question 10

A solenoid 50 cm long with a radius of 5.0 cm has 800 turns.You find that it carries a current of 10 A.The magnetic flux through it is approximately

A)47 mWb
B)31 mWb
C)98 mWb
D)18 mWb
E)67 mWb

Question 11

Which of the following is a vector quantity?

A)current
B)charge
C)magnetic field
D)electric potential
E)magnetic flux

Question 12

Use the following figure for the next problem.

-A rectangle is bent on two sides at 90 ^$\circ$ so that one end lies along the xy-plane while the other end lies along the xz-plane.The length a = 10 cm and b = 30 cm.At t = 0,a magnetic field of strength B = 0.1 T lies in the yz-plane and points at an angle $\theta$ = 30 ^$\circ$ and 10 ms later the field points in the opposite direction.The EMF induced in the rectangle is

A)10.4 V
B)6.0 V
C)12 V
D)8.2 V
E)None of these is correct.

Question 13

According to Faraday's law,a necessary and sufficient condition for an electromotive force to be induced in a closed circuit loop is the presence in the loop of

A)a magnetic field.
B)magnetic materials.
C)an electric current.
D)a time-varying magnetic flux.
E)a time-varying magnetic field.

Question 14

A 100-turn coil has a radius of 7.50 cm and a resistance of 50.0 $\Omega$ .At what rate must a perpendicular magnetic field change to produce a current of 5.00 A in the coil?

A)275 T/s
B)134 T/s
C)329 T/s
D)141 T/s
E)106 T/s

Question 15

The instantaneous induced EMF in a coil of wire located in a magnetic field

A)depends on the time rate of change of flux through the coil.
B)depends on the instantaneous value of flux through the coil.
C)is independent of the area of the coil.
D)is independent of the number of turns of the coil.
E)is determined by the resistance in series with the coil.

Question 16

A 3.0-cm by 5.0-cm rectangular coil has 100 turns.Its axis makes an angle of 55º with a uniform magnetic field of 0.35 T.What is the magnetic flux through this coil?

A)3.0 $\times$ 10^-4 Wb
B)4.3 $\times$ 10^-4 Wb
C)3.0 $\times$ 10^-2 Wb
D)4.3 $\times$ 10^-2 Wb
E)5.3 $\times$ 10^-2 Wb

Question 17

The magnetic flux through a 50-cm-long solenoid that has 500 turns of radius 3.0 cm is 3.0 $\times$ 10^-2 Wb.Calculate the current through the solenoid.

A)53 A
B)5.4 A
C)17 A
D)1.3 A
E)34 A

Question 18

You can change the magnetic flux through a given surface by

A)changing the magnetic field.
B)changing the surface area over which the magnetic field is distributed.
C)changing the angle between the magnetic field and surface in question.
D)any combination of a through c.
E)none of these strategies.

Question 19

A circular loop of radius R has 50 turns.It lies in the xy plane.A time dependent magnetic field where A is a constant,passes through the loop.The EMF induced in the loop is

A)50 $\pi$ AR² sin ( $\omega$ t)
B)50 $\pi$ AR² cos ( $\omega$ t)
C)50 $\pi$$\omega$ AR² sin ( $\omega$ t)
D)50 $\pi$$\omega$ AR² cos ( $\omega$ t)
E)None of these is correct.

Question 20

You place a coil that has 200 turns and a cross-sectional area of 0.050 m² so that its plane is normal to a field of 3.0 T.If the field is uniformly decreased to zero in 5.0 s,what EMF is induced in the coil?

A)0.15 kV
B)0.12 kV
C)6.0 V
D)50 mV
E)10 mV

Question 21

You place a single loop of wire 0.50 m by 0.30 m perpendicular to a field of 2.0 T.In 30 ms you turn the loop until it is parallel with the field.The average emf induced in this loop is

A)0.30 V
B)10 V
C)5.0 V
D)67 V
E)20 V

Question 22

Use the following figure for the next problem.
A rectangular coil moving at a constant speed v enters a region of uniform magnetic field from the left.While the coil is exiting the field on the right,the direction of the magnetic force is

A)1
B)2
C)3
D)4
E)5

Question 23

Which law does the following statement express? "In all cases of electromagnetic induction,the induced voltages have a direction such that the currents they produce oppose the effect that produces them."

A)Maxwell's law
B)Fleming's rule
C)Lenz's law
D)Gauss's law
E)Ampère's law

Question 24

A 25-cm long conducting rod moves at a speed of 12 m/s in a plane perpendicular to a uniform magnetic field of magnitude 0.080 T.What is the induced potential difference between the ends of the rod?

A)24 V
B)2.4 V
C)0.24 V
D)0.60 kV
E)6.0 V

Question 25

Use the following figure for the next problem:
A classic demonstration illustrating eddy currents is performed by dropping a permanent magnet inside a conducting cylinder.The magnet does not go into free fall.Instead it reaches terminal velocity and can take a few seconds to drop a length of about a meter.Suppose the mass of the magnet is 70 g and it has a terminal velocity of 10 cm/s.The length of the pipe is 80 cm.What is the magnitude of the magnetic force on the magnet when it is falling at the terminal velocity?

A)0.35 N
B)0.79 N
C)0.97 N
D)0.69 N
E)None of these is correct.

Question 26

For the current in a stationary circuit to induce a current in an independent stationary circuit,it is necessary for the first circuit to have

A)a steady current.
B)a large current.
C)no current.
D)a changing current.
E)None of these is correct.

Question 27

Use the following figure for the next problem:

-A classic demonstration illustrating eddy currents is performed by dropping a permanent magnet inside a conducting cylinder.The magnet does not go into free fall.Instead it reaches terminal velocity and can take a few seconds to drop a length of about a meter.Suppose the mass of the magnet is 70 g and width of 1.0 cm.It falls with a terminal velocity of 10 cm/s and the length of the pipe is 80 cm.The magnitude of the Joule heating from the eddy currents is approximately

A)0.55 J
B)8.8 $\times$ 10^-5 J
C)1.1 J
D)1.8 $\times$ 10^-4 J
E)None of these is correct.

Question 28

A coil consisting of 20 turns of wire around the periphery of a rectangular frame 10 cm by 5.0 cm is moved from a position near a magnet where the average flux density is 1.0 mT to another position where the average is 11 mT.If this motion takes place in
1.0 s,the average EMF induced in the coil is

A)0.10 kV
B)1.0 kV
C)1.0 mV
D)0.10 MV
E)10 mV

Question 29

A conducting loop around a bar magnet begins to move away from the magnet.Which of the following statements is true?

A)The magnet and the loop repel one another.
B)The magnet and the loop attract one another.
C)The magnet is attracted,but the loop is repelled.
D)The magnet is repelled,but the loop is attracted.
E)The magnet and loop neither attract nor repel one another.

Question 30

A rectangular coil of length l = 20 cm and width w = 15 cm is moving at a constant speed v = 5 m/s.It enters a region of uniform magnetic field B = 0.2 T from the left.While the coil is completely immersed in the field,the voltage across points a and b is

A)0.20 V
B)0.15 V
C)-0.20 V
D)-0.15 V
E)zero

Question 31

A straight conductor 10 cm long is perpendicular to a uniform magnetic field of flux density 2.0 mT.When the conductor carries a current of 5.0 A,the force exerted on it by the field is

A)0.25 kN
B)40 $\mu$ N
C)1.0 mN
D)zero
E)5.0 mN

Question 32

A metal disk rotates about its central axis at an angular frequency of 800 radians per second in a uniform magnetic field of 0.8 T.The diameter of the disk is 8 cm.What is the magnitude of the voltage difference between the center and edge of the disk?

A)0 V
B)0.80 V
C)0.51 V
D)1.0 V
E)3.1 V

Question 33

A circular loop,of radius 15 cm and negligible resistance,is sitting in a perpendicular magnetic field of 0.1 T.If the magnetic field strength changes to a value of 0.5 T in 0.5 s,calculate the induced current in the loop if it is in series with a 20 ohm resistor.

A)5.7 $\times$ 10^-2 A
B)1.2 $\times$ 10^-2 A
C)2.8 $\times$ 10^-3 A
D)6.0 $\times$ 10^-4 A
E)1.1 A

Question 34

A square coil of wire with side 9.0 cm and 8 turns sits in a uniform magnetic field of 2 T that is perpendicular to the plane of the coil.If an EMF of 0.5 V is induced in the coil when the magnetic field is reversed,find the time taken for the field reversal.

A)0.26 s
B)1.0 s
C)5.8 s
D)1.6 s
E)0.52 s

Question 35

What is the average induced EMF between the ends of the wings of a plane flying at a speed of 500 km/hr when the vertical component of Earth's magnetic field is 3 $\times$ 10^-5 T? The distance between the wingtips is 25 m.

A)0.20 V
B)0.050 V
C)6.0 V
D)0.10 V
E)none of the above

Question 36

Use the following figure for the next problem.
A rectangular coil moving at a constant speed v enters a region of uniform magnetic field from the left.While the coil is entering the field,the direction of the magnetic force is

A)1
B)2
C)3
D)4
E)5

Question 37

The motion of a conducting rod through a magnetic field creates a motional EMF E.If the rod accelerates to twice the speed,what will the motional EMF be?

A) $\varepsilon$
B)2 $\varepsilon$
C) $\varepsilon$ /2
D)4 $\varepsilon$
E) $\varepsilon$ ²

Question 38

Two identical bar magnets are dropped from equal heights.Magnet A is dropped over bare earth and magnet B over a metal plate.Which magnet strikes first?

A)magnet A
B)magnet B
C)both strike at the same time
D)whichever has its N pole toward the ground
E)whichever has its S pole toward the ground

Question 39

Eddy currents

A)are a consequence of changing magnetic flux.
B)generate heat and result in power loss.
C)can be used for damping and braking purposes.
D)are described by both Faraday's and Lenz's laws.
E)All of these are correct.

Question 40

The plane of a wire loop with an area of 0.20 m² is perpendicular to a magnetic field of 50 mT.In 40 ms you rotate the loop 90º so that its plane is parallel to the magnetic field.The average EMF induced in the loop is

A)0.25 V
B)6.0 V
C)3.0 V
D)4.0 V
E)1.3 V

Question 41

A coil of self inductance 7.5 mH and resistance of 30 $\Omega$ is placed across the terminals of a 12-V battery of negligible internal resistance.The current in this circuit after 50 $\mu$ s is approximately

A)73 mA
B)47 mA
C)28 mA
D)51 mA
E)19 mA

Question 42

An LR circuit has a resistance R = 25 $\Omega$ ,an inductance L = 5.4 mH,and a battery of EMF = 9.0 V.How much energy is stored in the inductance of this circuit when a steady current is achieved?

A)zero
B)0.35 J
C)0.35 mJ
D)0.70 mJ
E)0.97 mJ

Question 43

A region of space contains a magnetic field of 500 G and an electric field of 3 $\times$ 10⁶ N/C.The total energy density in a cubical box of side = 20 cm in this region is

A)19.4 kJ/m³
B)12.2 kJ/m³
C)1.03 kJ/m³
D)66.9 J/m³
E)24.6 J/m³

Question 44

What is the time constant of an RL circuit with a resistance R = 25 $\Omega$ and an inductance L = 5.4 mH?

A)7.4 s
B)4.6 s
C)0.14 s
D)0.22 ms
E)1.5 ms

Question 45

A region of space contains a magnetic field of 500 G and an electric field of 3 $\times$ 10⁶ N/C.The magnetic energy density in a cubical box of side = 20 cm in this region is

A)550 J/m³
B)670 J/m³
C)864 J/m³
D)995 J/m³
E)None of these is correct.

Question 46

How much does the energy stored in an inductor change if the current through the inductor is doubled?

A)it is the same
B)it is doubled
C)it is quadrupled
D)it is halved
E)it is quartered

Question 47

A coil with a self-inductance of 6.5 H carries a current that is changing at a rate of 50 A/s.What is the induced EMF in the coil?

A)0.13 V
B)7.7 V
C)32 V
D)65 V
E)0.32 kV

Question 48

A device used chiefly for storing energy in a magnetic field is

A)an inductor.
B)a resistor.
C)a capacitor.
D)a galvanometer.
E)a dielectric.

Question 49

The current in an RL circuit is zero at time t = 0 and increases to half its final value in 6.0 s.The time constant of this circuit is approximately

A)6.0 s
B)12 s
C)8.7 s
D)3.0 s
E)9.8 s

Question 50

How many turns are needed in a solenoid of radius 10 cm and length 20 cm for its self-inductance to be 6.0 H?

A)30
B)74
C)500
D)550
E)5500

Question 51

A solenoid is 15 cm long,has a radius of 5 cm,and has 400 turns.If it carries a current of 4 A,the magnetic energy stored in the solenoid is

A)84.2 mJ
B)0.562 J
C)3.37 J
D)12.6 mJ
E)None of these is correct.

Question 52

After you measure the self-inductance of a coil,you unwind it and then rewind half the length of wire into a coil with the same diameter but half the number of turns.How does this change the self-inductance?

A)it is the same
B)it is doubled
C)it is quadrupled
D)it is halved
E)it is quartered

Question 53

A region of space contains a magnetic field of 500 G and an electric field of 3 $\times$ 10⁶ N/C.The electrical energy density in a cubical box of side = 20 cm in this region is

A)19.9 J/m³
B)39.8 J/m³
C)54.8 J/m³
D)66.9 J/m³
E)74.6 J/m³

Question 54

The self-inductance of a wire coil is a proportionality constant that relates

A)electric field to current.
B)electric flux to current.
C)magnetic flux to current.
D)magnetic field to current.
E)voltage to current.

Question 55

The current in an RL circuit is zero at time t = 0 and increases to 75% of its final value in 4.5 s.The time constant of this circuit is approximately

A)6.0 s
B)12 s
C)8.7 s
D)3.3 s
E)9.8 s

Question 56

Which of the following statements about superconductors is true?

A)Both type I and type II superconductors have zero resistance below the critical temperature T_c.
B)In type I superconductors,the magnetic is expelled from the superconductors below the critical temperature T_c.
C)In type II superconductors,the magnetic is expelled from the superconductors below the critical temperature T_c and below a certain field B_c1.
D)Superconductors are prefect diamagnetics.
E)All the above statements are true.