Question 1

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 2

What resistance should be added in series with a 3.0-H inductor to complete an LR circuit with a time constant of   ?

Accepted Answer

A)  0.75 k Ω 
B)  12 Ω 
C)  0.75 Ω 
D)  2.5 Ω 
A)  0.75 k Ω 
B)  12 Ω 
C)  0.75 Ω 
D)  2.5 Ω

Question 3

As shown in the figure, a wire and a 10-Ω resistor are used to form a circuit in the shape of a square, 20 cm by 20 cm. A uniform but nonsteady magnetic field is directed into the plane of the circuit. The magnitude of the magnetic field is decreased from 1.50 T to 0.50 T in a time interval of 63 ms. The average induced current and its direction through the resistor, in this time interval, are closest to

Accepted Answer

A)  63 mA, from b to a. 
B)  38 mA, from b to a. 
C)  63 mA, from a to b. 
D)  38 mA, from a to b. 
E)  95 mA, from a to b. 
A)  63 mA, from b to a. 
B)  38 mA, from b to a. 
C)  63 mA, from a to b. 
D)  38 mA, from a to b. 
E)  95 mA, from a to b.

Question 4

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.

Question 5

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

Question 6

A series circuit consists of a 0.55-H inductor with internal resistance of 8.0 Ω connected in series with a 4.0-Ω resistor, an open switch, and an ideal 12-V battery.
(a) When the switch is closed, what is the initial current through the 4.0-Ω resistor?
(b) What is the current through the 4.0-Ω resistor a very long time after the switch is closed?

Accepted Answer

(a) 0.00 A

Question 7

An LR circuit contains an ideal 60-V battery, a 51-H inductor having no resistance, a 21-Ω resistor, and a switch S, all in series. Initially, the switch is open and has been open for a very long time. At time t = 0 s, the switch is suddenly closed. When the voltage across the resistor is equal to the voltage across the inductor, what is the current in the circuit?

Accepted Answer

A)  1.4 A 
B)  0.57 A 
C)  1.1 A 
D)  0.86 A 
E)  1.7 A 
A)  1.4 A 
B)  0.57 A 
C)  1.1 A 
D)  0.86 A 
E)  1.7 A

Question 8

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 9

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 10

A charged capacitor is connected to an ideal inductor. At time t = 0, the charge on the capacitor is equal to 6.00 μC. At time t = 2.00 ms the charge on the capacitor is zero for the first time. What is the amplitude of the current at that same instant?

Accepted Answer

A)  2.38 mA 
B)  4.71 mA 
C)  0.780 mA 
D)  1.53 mA 
E)  1.19 mA 
A)  2.38 mA 
B)  4.71 mA 
C)  0.780 mA 
D)  1.53 mA 
E)  1.19 mA

Question 11

A charged capacitor is connected to an ideal inductor to form an LC circuit with a frequency of oscillation f = 1.6 Hz. At time t = 0 the capacitor is fully charged. At a given instant later the charge on the capacitor is measured to be 3.0 μC and the current in the circuit is equal to 75 μA. What is the maximum charge of the capacitor?

Accepted Answer

A)  6.0 µC 
B)  10 µC 
C)  8.0 µC 
D)  2.0 µC 
E)  4.0 µC 
A)  6.0 µC 
B)  10 µC 
C)  8.0 µC 
D)  2.0 µC 
E)  4.0 µC

Question 12

What is the energy density in the magnetic field 25 cm from a long straight wire carrying a current of 12 A? (μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

A)  7.3 × 10-5 J/m3 
B)  3.7 × 10-5 J/m3 
C)  3.6 × 10-4 J/m3 
D)  1.2 × 10-4 J/m3 
E)  The density cannot be determined without knowing the volume. 
A)  7.3 × 10-5 J/m3 
B)  3.7 × 10-5 J/m3 
C)  3.6 × 10-4 J/m3 
D)  1.2 × 10-4 J/m3 
E)  The density cannot be determined without knowing the volume.

Question 13

An LR circuit contains an ideal 60-V battery, a 42-H inductor having no resistance, a 24-Ω resistor, and a switch S, all in series. Initially, the switch is open and has been open for a very long time. At time t = 0 s, the switch is suddenly closed. How long after closing the switch will the potential difference across the inductor be 24 V?

Accepted Answer

A)  1.6 s 
B)  1.4 s 
C)  1.8 s 
D)  1.9 s 
E)  2.1 s 
A)  1.6 s 
B)  1.4 s 
C)  1.8 s 
D)  1.9 s 
E)  2.1 s

Question 14

For the circuit shown in the figure, the switch has been open for a very long time.   
(a) What is the potential drop across the 15.0-mH inductor just after closing the switch?
(b) What is the potential drop across the 70.0-µF capacitor after the switch has been closed for a very long time?

Accepted Answer

(a) 150.0

Question 15

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. 
E)  570.0 mJ. 
A)  570 mJ. 
B)  29 mJ. 
C)  10 mJ. 
D)  100 mJ. 
E)  570.0 mJ.

Question 16

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 17

A conducting bar slides without friction on two parallel horizontal rails that are 50 cm apart and connected by a wire at one end. The resistance of the bar and the rails is constant and equal to 0.10 Ω. A uniform magnetic field is perpendicular to the plane of the rails. A 0.080-N force parallel to the rails is required to keep the bar moving at a constant speed of 0.50 m/s. What is the magnitude of the magnetic field?

Accepted Answer

A)  0.10 T 
B)  0.25 T 
C)  0.36 T 
D)  0.54 T 
E)  0.93 T 
A)  0.10 T 
B)  0.25 T 
C)  0.36 T 
D)  0.54 T 
E)  0.93 T

Question 18

The primary coil of a transformer has 100 turns and its secondary coil has 400 turns. If the ac voltage applied to the primary coil is 120 V, what voltage is present in its secondary coil?

Accepted Answer

A)  100 V 
B)  30 V 
C)  70 V 
D)  480 V 
E)  400 V 
A)  100 V 
B)  30 V 
C)  70 V 
D)  480 V 
E)  400 V

Question 19

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 20

For the circuit shown in the figure, the inductors have no appreciable resistance and the switch has been open for a very long time.   
(a) The instant after closing the switch, what is the current through the 60.0-Ω resistor?
(b) The instant after closing the switch, what is the potential difference across the 15.0-mH inductor?
(c) After the switch has been closed and left closed for a very long time, what is the potential drop across the 60.0-Ω resistor?

Accepted Answer

(a) 1.43 A

Exam 33: Electromagnetic Induction

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

What resistance should be added in series with a 3.0-H inductor to complete an LR circuit with a time constant of ?

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

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 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?

A charged capacitor is connected to an ideal inductor. At time t = 0, the charge on the capacitor is equal to 6.00 μC. At time t = 2.00 ms the charge on the capacitor is zero for the first time. What is the amplitude of the current at that same instant?

What is the energy density in the magnetic field 25 cm from a long straight wire carrying a current of 12 A? (μ0 = 4π × 10-7 T ∙ m/A)

For the circuit shown in the figure, the switch has been open for a very long time. (a) What is the potential drop across the 15.0-mH inductor just after closing the switch? (b) What is the potential drop across the 70.0-µF capacitor after the switch has been closed for a very long time?

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)

The primary coil of a transformer has 100 turns and its secondary coil has 400 turns. If the ac voltage applied to the primary coil is 120 V, what voltage is present in its secondary coil?

Concepts of Motion

Kinematics in One Dimension

Vectors and Coordinate Systems

Kinematics in Two Dimensions

Force and Motion

Dynamics I: Motion Along a Line

Newtons Third Law

Dynamics Ii: Motion in a Plane

Impulse and Momentum

Energy

Work

Rotation of a Rigid Body

Newtons Theory of Gravity

Oscillations

Fluids and Elasticity

A Macroscopic Description of Matter

Work, Heat, and the First Law of Thermodynamics

The Micromacro Connection

Heat Engines and Refrigerators

Traveling Waves

Superpositions

Wave Optics

Ray Optics

Optical Instruments

Electric Charges and Forces

The Electric Field

Gausss Law

The Electric Potential

Potential and Field

Current and Resistance

Fundamentals of Circuits

The Magnetic Field

Electromagnetic Fields and Waves

Ac Circuits

Relativity

The Foundations of Modern Physics

Quantization

Wave Functions and Uncertainty

One-Dimensional Quantum Mechanics

Atomic Physics

Nuclear Physics

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?

What is the energy density in the magnetic field 25 cm from a long straight wire carrying a current of 12 A? (μ₀ = 4π × 10^-7 T ∙ m/A)

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)