Question 1

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. B

Question 2

In the figure, the inner loop carries a clockwise current I that is increasing. The resistor R is in the outer loop and both loops are in the same plane. 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. A

Question 3

In the figure, a copper bar is in contact with a pair of parallel metal rails and is in motion with velocity ν. A uniform magnetic field is present pointing downward, as shown. The bar, the rails, and the resistor R are all in the same plane. 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. C

Question 4

Which of the following statements about inductors are correct? There may be more than one correct choice.

Accepted Answer

A)  When it is connected in a circuit, an inductor always resists having current flow through it. 
B)  Inductors store energy by building up charge. 
C)  When an inductor and a resistor are connected in series with a DC battery, the current in the circuit is reduced to zero in one time constant. 
D)  An inductor always resists any change in the current through it. 
E)  When an inductor and a resistor are connected in series with a DC battery, the current in the circuit is zero after a very long time. 
A)  When it is connected in a circuit, an inductor always resists having current flow through it. 
B)  Inductors store energy by building up charge. 
C)  When an inductor and a resistor are connected in series with a DC battery, the current in the circuit is reduced to zero in one time constant. 
D)  An inductor always resists any change in the current through it. 
E)  When an inductor and a resistor are connected in series with a DC battery, the current in the circuit is zero after a very long time.

Question 5

The coil in a 60-Hz ac generator has 125 turns, each having an area of 3.0 × 10-2 m2 and is rotated in a uniform 0.12-T magnetic field. What is the peak output voltage of this generator?

Accepted Answer

A)  170 V 
B)  120 V 
C)  200 V 
D)  110 V 
E)  220 V 
A)  170 V 
B)  120 V 
C)  200 V 
D)  110 V 
E)  220 V

Question 6

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 7

For a long ideal solenoid having a circular cross-section, the magnetic field strength within the solenoid is given by the equation B(t) = 5.0t T, where t is time in seconds. If the induced electric field outside the solenoid is 1.1 V/m at a distance of 2.0 m from the axis of the solenoid, find the radius of the solenoid.

Accepted Answer

A)  0.30 m 
B)  77 m 
C)  0.94 m 
D)  9.0 m 
A)  0.30 m 
B)  77 m 
C)  0.94 m 
D)  9.0 m

Question 8

A circular loop of radius 0.10 m is rotating in a uniform external magnetic field of 0.20 T. Find the magnetic flux through the loop due to the external field when the plane of the loop and the magnetic field vector are
(a) parallel.
(b) perpendicular.
(c) at an angle of 30° with each other.

Accepted Answer

(a) zero

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

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 11

A coil of 160 turns and area 0.20 m2 is placed with its axis parallel to a magnetic field of initial magnitude 0.40 T. The magnetic field changes uniformly from 0.40 T in the +x direction to 0.40 T in the -x direction in 2.0 s. If the resistance of the coil is 16 Ω, at what rate is power generated in the coil?

Accepted Answer

A)  5.0 W 
B)  10 W 
C)  15 W 
D)  20 W 
E)  25 W 
A)  5.0 W 
B)  10 W 
C)  15 W 
D)  20 W 
E)  25 W

Question 12

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 13

A large magnetic flux change through a coil must induce a greater emf in the coil than a small flux change.

Accepted Answer

A) True 
 B)False

Question 14

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.

Question 15

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 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

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

Question 18

A 200-loop coil of cross sectional area 8.5 cm2 lies in the plane of the page. An external magnetic field of 0.060 T is directed out of the plane of the page. The external field decreases to 0.020 T in 12 milliseconds.
(a) What is the magnitude of the change in the external magnetic flux enclosed by the coil?
(b) What is the magnitude of the average voltage induced in the coil as the external flux is changing?
(c) If the coil has a resistance of 4.0 ohms, what is the magnitude of the average current in the coil?

Accepted Answer

(a) 4.0 ×

Question 19

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.

Question 20

A 50-cm wire placed in an east-west direction is moved horizontally to the north with a speed of 2.0 m/s. The horizontal component of the earth's magnetic field at that location is 25 μT toward the north and the vertical component is 50μT downward. What is the emf induced between the ends of the wire?

Accepted Answer

A)  10 µV 
B)  20 µV 
C)  30 µV 
D)  40 µV 
E)  50 µV 
A)  10 µV 
B)  20 µV 
C)  30 µV 
D)  40 µV 
E)  50 µV

Exam 28: Electromagnetic Induction

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

In the figure, the inner loop carries a clockwise current I that is increasing. The resistor R is in the outer loop and both loops are in the same plane. The induced current through the resistor R is

In the figure, a copper bar is in contact with a pair of parallel metal rails and is in motion with velocity ν. A uniform magnetic field is present pointing downward, as shown. The bar, the rails, and the resistor R are all in the same plane. The induced current through the resistor R is

Which of the following statements about inductors are correct? There may be more than one correct choice.

The coil in a 60-Hz ac generator has 125 turns, each having an area of 3.0 × 10-2 m2 and is rotated in a uniform 0.12-T magnetic field. What is the peak output voltage of this generator?

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

A circular loop of radius 0.10 m is rotating in a uniform external magnetic field of 0.20 T. Find the magnetic flux through the loop due to the external field when the plane of the loop and the magnetic field vector are (a) parallel. (b) perpendicular. (c) at an angle of 30° with each other.

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?

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

A large magnetic flux change through a coil must induce a greater emf in the coil than a small flux change.

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?

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 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?

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

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Filters

The coil in a 60-Hz ac generator has 125 turns, each having an area of 3.0 × 10^-2m² and is rotated in a uniform 0.12-T magnetic field. What is the peak output voltage of this generator?

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?