PHYS131 - Ch. 21 Review Questions

A closed loop conductor with radius 3.0 m is located in a changing magnetic field. If the maximum emf induced in the loop is 2.2 V, what is the maximum rate at which the magnetic field strength is changing if the magnetic field is oriented perpendicular to the plane in which the loop lies? 13 T/s 0.08 T/s 4.2 T/s 0.039 T/s

0.08 T/s

A circular conducting loop with a radius of 0.75 m and a small gap filled with a 9.00 Ω resistor is oriented in the xy-plane. If a magnetic field of 1.5 T, making an angle of 30° with the z-axis, increases to 15.0 T, in 3.5 s, what is the magnitude of the current that will be caused to flow in the conductor? 0.21 A 0.073 A 0.38 A 0.66 A

0.66 A

What resistance should be added in series with a 4.0 H inductor to complete an RL circuit with a 3.0 ms time constant? 12 Ω 1.3 k Ω 1.3 Ω 2.5 Ω

1.3 k Ω

A series RL circuit has a 5 k Ω resistor and a 8 mH inductor. What is the time constant for the circuit? 0.47 μs 3.69 s 40 s 1.6 μs

1.6 μs

A 3 A current passes through an inductor. If the inductor stores 12 J of energy, what is the inductance? 36 H 54 H 2.67 H 2.8 H

2.67 H

A conductor is formed into a loop that encloses an area of 1 m2. The loop is oriented at a 30.0° angle with the xy-plane. A varying magnetic field is oriented parallel to the z-axis. If the maximum emf induced in the loop is 22 V, what is the maximum rate at which the magnetic field strength is changing? 11 T/s 25 T/s 44 T/s 19 T/s

25 T/s

The current flowing through a circuit is changing at a rate of 7 A/s. If the circuit contains a 650 H inductor, what is the emf across the inductor? 9100 V 650 V 4550 V

4550 V

In the figure, a bar is in contact with a pair of parallel rails. A steady, uniform, magnetic field B is present. The bar is in motion with velocity ν. The polarity of the induced emf in terminals X and Y is: X is positive and Y is negative X and Y are at the same potential Y is positive and X is negative

X and Y are at the same potential

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: X is positive and Y is negative Y is positive and X is negative X and Y are at the same potential

Y is positive and X is negative

In the figure, a straight wire carries a steady current I. A bar is in contact with a pair of rails and is in motion with velocity ν. The polarity of the induced emf in terminals X and Y is: X is positive and Y is negative X and Y are at the same potential Y is positive and X is negative

Y is positive and X is negative

While a magnet is moved toward the end of a solenoid (as shown in the figure), a voltage difference is induced between the two ends of the solenoid wire. The voltage difference would be larger if a. the solenoid contained more loops (while having the same length). b. The bar magnet produced a stronger magnetic field. c. the speed of the magnet were increased. d. All of the above statements are true. c. Only two of the above statements are true.

all of the above statements are true

A 5 H inductor carries a current of 2 amps. How can a self-induced EMF of 50 volts be made to appear across the inductor? a. Break the circuit instantaneously. b. Change the current at the rate of 10 amps/sec. c. Change the current uniformly to zero in 20 seconds. d. Change the current to 10 amps. e. None of these.

b. Change the current at the rate of 10 amps/sec.

A 1.4 m conductor is formed into a square and placed in the horizontal xy-plane. A magnetic field is oriented 30.0° above the horizontal with a strength of 1.3 T. What is the magnetic flux through the conductor? 0.14 T∙m2 1.3 T∙m2 0.08 T∙m2 0.32 T∙m2

c

A circular wire 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. There is no induced current in the wire ring. b. There is an induced current in the wire ring, directed in a counterclockwise orientation. c. There is an induced current in the wire ring, directed in clockwise orientation.

c. There is an induced current in the wire ring, directed in clockwise orientation

If you hold a sheet of copper in a strong permanent magnet, with the plane of the sheet perpendicular to the magnetic field, and quickly jerk it out, a. you will experience a magnetic force assisting your action. b. you will feel no magnetic force. c. you will experience a magnetic force opposing your action. d. any force you feel will be due mainly to iron impurities in the copper, since copper itself is not magnetic. e. None of these are true.

c. you will experience a magnetic force opposing your action.

A square loop of wire is pulled upward out of the space between the poles of a magnet, as shown in the figure. As this is done, the current induced in this loop, as viewed from the N pole of the magnet, will be directed As this is done, the current induced in this loop, as viewed from the N pole of the magnet, will be directed a. clockwise. b. counterclockwise. c. zero.

clockwise

The slide wire of the variable resistor in the figure (Figure 1) is moved steadily to the right, increasing the resistance in the circuit. While this is being done, the current induced in the small circuit A is directed While this is being done, the current induced in the small circuit A is directed a. clockwise. b. counterclockwise. c. zero.

counterclockwise

A metal loop moves at constant velocity toward a long wire carrying a steady current I, as shown in (Figure 1) The current induced in the loop is directed clockwise. zero. directed counterclockwise.

directed clockwise

A loop of wire is situated inside a large solenoid, with the plane of the loop initially perpendicular to the axis of the solenoid. Current can be made to flow through the loop of wire if a. the current flowing through the solenoid is decreasing with time. b. the loop of wire is rotating within the solenoid, and a constant current is flowing through the solenoid wire. c. a constant current is flowing through the solenoid wire. d. All of the above statements are true. e. Only two of the above statements are true.

e. Only two of the above statements are true.

The two solenoids in the figure (Figure 1) are coaxial and fairly close to each other. While the resistance of the variable resistor in the left-hand solenoid is increased at a constant rate, the induced current through the resistor R will flow from b to a. flow from a to b. be zero because the rate is constant.

flow from b to a

In the figure, a bar is in contact with a pair of parallel rails. A steady, uniform, magnetic field, perpendicular to the plane of the rails, is present. The bar is in motion with velocity ν. The induced current through the resistor R is: from b to a from a to b zero

from a to b

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

from a to b

In the figure, a battery supplies a steady current to the solenoid on the left. The two solenoids are moving toward each other. The induced current through the resistor R is: from b to a from a to b zero

from a to b

In the figure, a loop carries a steady current I. A bar is in contact with a pair of circular rails, and rotates about the center of the loop. The induced current through the resistor R is: from b to a from a to b zero

from b to a

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

from b to a

In the figure, one end of a bar is in contact with a circular rail and the other end is pivoted at P. A steady, uniform, magnetic field B is present. The bar rotates about P. The induced current through the resistor R is: from a to b zero from b to a

from b to a

A metal ring is oriented with the plane of its area perpendicular to a spatially uniform magnetic field that increases at a steady rate. After the radius of the ring is doubled, while the rate of increase of the field is cut in half, the emf induced in the ring in half, the emf induced in the ring a. decreases by a factor of 2. b. increases by a factor of 4. c. increases by a factor of 2. d. remains the same.

increase by factor of 2

A vertical bar moves horizontally at constant velocity through a uniform magnetic field, as shown in (Figure 1) . We observe that point b is at a higher potential than point a. We can therefore conclude that the magnetic field must have a component that is directed a. vertically upward. b. vertically downward. c. perpendicular to the plane of the paper, outward. d. perpendicular to the plane of the paper, inward.

perpendicular to the plane of the paper, inward

In the figure, a coil of wire is placed on the axis of a solenoid carrying a DC current. Which of the following will NOT result in an EMF being induced in the coil? Change the current in the solenoid. Rotate the coil about the x-axis. Rotate the coil about the y-axis. Rotate the coil about the z-axis. Move the coil toward point P.

rotate the coil about the z-axis

A steady current of 1.50 A flows through the solenoid shown in the figure (Figure 1) . The current induced in the loop, as viewed from the right, is directed counterclockwise. zero. directed clockwise.

zero

In the figure, a bar is in contact with a pair of parallel rails and is in motion with velocity ν. A uniform magnetic field is present. The induced current through the resistor R is: from a to b zero from b to a

zero

In the figure, a long bar slides on two contact points and is in motion with velocity ν. A steady, uniform, magnetic field B is present. The induced current through the resistor R is: from a to b from b to a zero

zero

In the figure, a straight wire carries a steady current I. A bar is in contact with a pair of circular rails, and rotates about the straight wire. The induced current through the resistor R is: from b to a zero from a to b

zero