Question 1

In the figure,a C-shaped conductor is in a uniform magnetic field B,which is increasing.The polarity of the induced emf in terminals X and Y is

Accepted Answer

A)  X and Y are at the same potential. 
B)  X is positive and Y is negative. 
C)  X is negative and Y is positive. 
A)  X and Y are at the same potential. 
B)  X is positive and Y is negative. 
C)  X is negative and Y is positive. C

Question 2

In the figure,a straight wire carries a current I.The wire passes through the center of a toroidal coil.If the current in the wire is quickly reduced to zero,the induced current through the resistor R is

Accepted Answer

A)  from a to b. 
B)  from b to a. 
C)  There is no induced current through the resistor. 
A)  from a to b. 
B)  from b to a. 
C)  There is no induced current through the resistor. B

Question 3

A 2.0-m long conducting wire is formed into a square and placed in the horizontal xy-plane.A uniform magnetic field is oriented 30.0° above the horizontal with a strength of 9.0 T.What is the magnetic flux through the square?

Accepted Answer

A)  1.1 T • m2 
B)  1.9 T • m2 
C)  2.3 T • m2 
D)  18 T • m2 
A)  1.1 T • m2 
B)  1.9 T • m2 
C)  2.3 T • m2 
D)  18 T • m2 A

Question 4

A capacitor is charging in a simple RC circuit with a dc battery.Which one of the following statements about this capacitor is accurate?

Accepted Answer

A)  There is a magnetic field between the capacitor plates because charge travels between the plates by jumping from one plate to the other. 
B)  There is no magnetic field between the capacitor plates because no charge travels between the plates. 
C)  There is a magnetic field between the capacitor plates, even though no charge travels between them, because the magnetic flux between the plates is changing. 
D)  There is a magnetic field between the capacitor plates, even though no charge travels between them, because the electric flux between the plates is changing. 
E)  The magnetic field between the capacitor plates is increasing with time because the charge on the plates is increasing. 
A)  There is a magnetic field between the capacitor plates because charge travels between the plates by jumping from one plate to the other. 
B)  There is no magnetic field between the capacitor plates because no charge travels between the plates. 
C)  There is a magnetic field between the capacitor plates, even though no charge travels between them, because the magnetic flux between the plates is changing. 
D)  There is a magnetic field between the capacitor plates, even though no charge travels between them, because the electric flux between the plates is changing. 
E)  The magnetic field between the capacitor plates is increasing with time because the charge on the plates is increasing.

Question 5

In the figure,two solenoids are side by side.The switch S,initially open,is closed.The induced current through the resistor R is

Accepted Answer

A)  from a to b. 
B)  from b to a. 
C)  There is no induced current through the resistor. 
A)  from a to b. 
B)  from b to a. 
C)  There is no induced current through the resistor.

Question 6

You are designing a generator to have a maximum emf of 8.0 V. If the generator coil has 200 turns and a cross-sectional area of 0.030 m2,what should be the frequency of the generator in a uniform magnetic field of 0.030 T?

Accepted Answer

A)  7.1 Hz 
B)  7.5 Hz 
C)  8.0 Hz 
D)  22 Hz 
E)  44 Hz 
A)  7.1 Hz 
B)  7.5 Hz 
C)  8.0 Hz 
D)  22 Hz 
E)  44 Hz

Question 7

The three loops of wire shown in the figure are all subject to the same uniform magnetic field   that does not vary with time.Loop 1 oscillates back and forth as the bob in a pendulum,loop 2 rotates about a vertical axis,and loop 3 oscillates up and down at the end of a spring.Which loop,or loops,will have an emf induced in them?

Accepted Answer

A)  loop 1 only 
B)  loop 2 only 
C)  loop 3 only 
D)  loops 1 and 2 
E)  loops 2 and 3 
A)  loop 1 only 
B)  loop 2 only 
C)  loop 3 only 
D)  loops 1 and 2 
E)  loops 2 and 3

Question 8

A rectangular coil having N turns and measuring 15 cm by 25 cm is rotating in a uniform 1.6-T magnetic field with a frequency of 75 Hz.The rotation axis is perpendicular to the direction of the field.If the coil develops a sinusoidal emf of maximum value 56.9 V,what is the value of N?

Accepted Answer

A)  2 
B)  4 
C)  6 
D)  8 
E)  10 
A)  2 
B)  4 
C)  6 
D)  8 
E)  10

Question 9

The figure shows three metal coils labeled A,B,and C heading towards a region where a uniform static magnetic field exists.The coils move with the same constant velocity and all have the same resistance.Their relative sizes are indicated by the background grid.As they enter the magnetic field the coils will have an induced electric current in them.For which coil will the current be the greatest?

Accepted Answer

A)  A 
B)  B 
C)  C 
D)  The current is the same in all three cases since all the coils move with the same velocity. 
E)  There is no induced current in any of the coils since they move at constant velocity. 
A)  A 
B)  B 
C)  C 
D)  The current is the same in all three cases since all the coils move with the same velocity. 
E)  There is no induced current in any of the coils since they move at constant velocity.

Question 10

The figure shows a bar magnet moving vertically upward toward a horizontal coil.The poles of the bar magnets are labeled X and Y.As the bar magnet approaches the coil it induces an electric current in the direction indicated on the figure (counter-clockwise as viewed from above).What are the correct polarities of the magnet?

Accepted Answer

A)  X is a south pole, Y is a north pole. 
B)  X is a north pole, Y is a south pole. 
C)  Both X and Y are north poles. 
D)  Both X and Y are south poles. 
E)  The polarities of the magnet cannot be determined from the information given. 
A)  X is a south pole, Y is a north pole. 
B)  X is a north pole, Y is a south pole. 
C)  Both X and Y are north poles. 
D)  Both X and Y are south poles. 
E)  The polarities of the magnet cannot be determined from the information given.

Question 11

In the figure,two solenoids are approaching each other with speed v as shown.The induced current through the resistor R is

Accepted Answer

A)  from a to b. 
B)  from b to a. 
C)  There is no induced current through the resistor. 
A)  from a to b. 
B)  from b to a. 
C)  There is no induced current through the resistor.

Question 12

Suppose that you wish to construct a simple ac generator having an output of 12 V maximum when rotated at 60 Hz. A uniform magnetic field of 0.050 T is available. If the area of the rotating coil is
100 cm2,how many turns do you need?

Accepted Answer

A)  8 
B)  16 
C)  32 
D)  64 
E)  128 
A)  8 
B)  16 
C)  32 
D)  64 
E)  128

Question 13

A circular loop of wire lies in the plane of the paper.An increasing magnetic field points out of the paper.What is the direction of the induced current in the loop?

Accepted Answer

A)  counter-clockwise then clockwise 
B)  clockwise then counter-clockwise 
C)  clockwise 
D)  counter-clockwise 
E)  There is no current induced in the loop. 
A)  counter-clockwise then clockwise 
B)  clockwise then counter-clockwise 
C)  clockwise 
D)  counter-clockwise 
E)  There is no current induced in the loop.

Question 14

In the figure,a straight wire carries a steady current I perpendicular to the plane of the page.A bar is in contact with a pair of circular rails,and rotates about the straight wire.The direction of the induced current through the resistor R is

Accepted Answer

A)  from a to b. 
B)  from b to a. 
C)  There is no induced current through the resistor. 
A)  from a to b. 
B)  from b to a. 
C)  There is no induced current through the resistor.

Question 15

A circular metal ring is situated above a long straight wire,as shown in the figure.The straight wire has a current flowing to the right,and the current is increasing in time at a constant rate.Which statement is true?

Accepted Answer

A)  There is an induced current in the metal ring, flowing in a clockwise direction. 
B)  There is an induced current in the metal ring, flowing in a counter-clockwise direction. 
C)  There is no induced current in the metal ring because the current in the wire is changing at a constant rate. 
A)  There is an induced current in the metal ring, flowing in a clockwise direction. 
B)  There is an induced current in the metal ring, flowing in a counter-clockwise direction. 
C)  There is no induced current in the metal ring because the current in the wire is changing at a constant rate.

Question 16

A closed,circular loop has a counter-clockwise current flowing through it as viewed by a person on the right,as shown in the figure.If a second closed circular loop with the same radius approaches this loop with constant velocity along a common axis as shown,in what direction will a current flow in the approaching loop as viewed by the person on the right?

Accepted Answer

A)  clockwise 
B)  counter-clockwise 
C)  No current will be induced because the velocity of approach is constant. 
A)  clockwise 
B)  counter-clockwise 
C)  No current will be induced because the velocity of approach is constant.

Question 17

In the figure,a bar magnet moves away from the solenoid.The induced current through the resistor R is

Accepted Answer

A)  from a to b. 
B)  from b to a. 
C)  There is no induced current through the resistor. 
A)  from a to b. 
B)  from b to a. 
C)  There is no induced current through the resistor.

Question 18

At what rate would the current in a 100-mH inductor have to change to induce an emf of 1000 V in the inductor?

Accepted Answer

A)  100 A/s 
B)  1 A/s 
C)  1000 A/s 
D)  10,000 A/s 
E)  10 A/s 
A)  100 A/s 
B)  1 A/s 
C)  1000 A/s 
D)  10,000 A/s 
E)  10 A/s

Question 19

How much energy is stored in a room 3.0 m by 4.0 m by 2.4 m due to the earth's magnetic field with a strength of 5.0 × 10-5 T? (μ0 = 4π × 10-7 T • m/A)

Accepted Answer

A)  570 mJ. 
B)  29 mJ. 
C)  10 mJ. 
D)  100 mJ. 
A)  570 mJ. 
B)  29 mJ. 
C)  10 mJ. 
D)  100 mJ.

Question 20

A coil lies flat on a tabletop in a region where the magnetic field vector points straight up.The magnetic field vanishes suddenly.When viewed from above,what is the direction of the induced current in this coil as the field fades?

Accepted Answer

A)  counter-clockwise then clockwise 
B)  clockwise then counter-clockwise 
C)  clockwise 
D)  counter-clockwise 
E)  There is no current induced in the coil. 
A)  counter-clockwise then clockwise 
B)  clockwise then counter-clockwise 
C)  clockwise 
D)  counter-clockwise 
E)  There is no current induced in the coil.

Exam 29: Changing Magnetic Fields

In the figure,a C-shaped conductor is in a uniform magnetic field B,which is increasing.The polarity of the induced emf in terminals X and Y is

In the figure,a straight wire carries a current I.The wire passes through the center of a toroidal coil.If the current in the wire is quickly reduced to zero,the induced current through the resistor R is

A 2.0-m long conducting wire is formed into a square and placed in the horizontal xy-plane.A uniform magnetic field is oriented 30.0° above the horizontal with a strength of 9.0 T.What is the magnetic flux through the square?

A capacitor is charging in a simple RC circuit with a dc battery.Which one of the following statements about this capacitor is accurate?

In the figure,two solenoids are side by side.The switch S,initially open,is closed.The induced current through the resistor R is

You are designing a generator to have a maximum emf of 8.0 V. If the generator coil has 200 turns and a cross-sectional area of 0.030 m2,what should be the frequency of the generator in a uniform magnetic field of 0.030 T?

A rectangular coil having N turns and measuring 15 cm by 25 cm is rotating in a uniform 1.6-T magnetic field with a frequency of 75 Hz.The rotation axis is perpendicular to the direction of the field.If the coil develops a sinusoidal emf of maximum value 56.9 V,what is the value of N?

In the figure,two solenoids are approaching each other with speed v as shown.The induced current through the resistor R is

Suppose that you wish to construct a simple ac generator having an output of 12 V maximum when rotated at 60 Hz. A uniform magnetic field of 0.050 T is available. If the area of the rotating coil is 100 cm2,how many turns do you need?

A circular loop of wire lies in the plane of the paper.An increasing magnetic field points out of the paper.What is the direction of the induced current in the loop?

In the figure,a straight wire carries a steady current I perpendicular to the plane of the page.A bar is in contact with a pair of circular rails,and rotates about the straight wire.The direction of the induced current through the resistor R is

A circular metal ring is situated above a long straight wire,as shown in the figure.The straight wire has a current flowing to the right,and the current is increasing in time at a constant rate.Which statement is true?

In the figure,a bar magnet moves away from the solenoid.The induced current through the resistor R is

At what rate would the current in a 100-mH inductor have to change to induce an emf of 1000 V in the inductor?

How much energy is stored in a room 3.0 m by 4.0 m by 2.4 m due to the earth's magnetic field with a strength of 5.0 × 10-5 T? (μ0 = 4π × 10-7 T • m/A)

A coil lies flat on a tabletop in a region where the magnetic field vector points straight up.The magnetic field vanishes suddenly.When viewed from above,what is the direction of the induced current in this coil as the field fades?

Foundations

A: Foundations

Motion in One Dimension

Acceleration

Momentum

Energy

Principle of Relativity

Interactions

Force

Work

Motion in a Plane

Motion in a Circle

Torque

Gravity

Special Relativity

Periodic Motion

Waves in One Dimension

Waves in Two and Three Dimensions

Fluids

Entropy

Energy Transferred Thermally

Degradation of Energy

Electric Interactions

The Electric Field

Gausss Law

Work and Energy in Electrostatics

Charge Separation and Storage

Magnetic Interactions

Magnetic Fields of Charged Particles in Motion

Changing Electric Fields

Electric Circuits

Electronics

Ray Optics

Wave and Particle Optics

Filters

You are designing a generator to have a maximum emf of 8.0 V. If the generator coil has 200 turns and a cross-sectional area of 0.030 m²,what should be the frequency of the generator in a uniform magnetic field of 0.030 T?

Suppose that you wish to construct a simple ac generator having an output of 12 V maximum when rotated at 60 Hz. A uniform magnetic field of 0.050 T is available. If the area of the rotating coil is 100 cm²,how many turns do you need?

How much energy is stored in a room 3.0 m by 4.0 m by 2.4 m due to the earth's magnetic field with a strength of 5.0 × 10^-5 T? (μ₀ = 4π × 10^-7 T • m/A)