Physics- Chapter 14

A loop of wire enclosing an area of 0.03 m2 has a magnetic field passing through its plane at an angle to the plane. The component of the field perpendicular to the plane is 0.7 T, and the component parallel to the plane is 0.6 T. What is the magnetic flux through this coil? _____ T · m2

0.021

A straight segment of wire has a length of 30 cm and carries a current of 6 A. It is oriented at right angles to a magnetic field of 0.6 T. What is the magnitude of the magnetic force on this segment of wire? _____ N

1.08

A step-down transformer is to be used to convert an ac voltage of 120 V to 5 V to power an electric train. If there are 320 turns in the primary coil, how many turns should there be in the secondary coil? _____ turns

13.3

The magnetic force on a 26-cm straight segment of wire carrying a current of 4 A is 4.0 N. What is the magnitude of the component of magnetic field perpendicular to the wire? _____ T

3.85

A particle with a charge of 0.8 C is moving at right angles to a uniform magnetic field with a strength of 0.8 T. The velocity of the charge is 520 m/s. What is the magnitude of the magnetic force exerted on the particle? ____ N

332.8

Two long parallel wires, each carrying a current of 13 A, lie a distance of 8 cm from each other. What is the magnetic force per unit length exerted by one wire on the other? _____ N/m If the distance between the two wires is tripled, what is the new force per unit length? _____ N/m

4.22E-4 1.41E-4

A coil of wire with 80 turns and a cross-sectional area of 0.05 m2 lies with its plane perpendicular to a magnetic field of magnitude 5.0 T. The coil is rapidly removed from the magnetic field in a time of 0.2 s. (a) What is the initial magnetic flux through the coil? _____ T · m2 (b) What is the average value of the voltage induced in the coil? _____ V

a. 20 b. 100

Two coils of wire are identical except that coil A has twice as many turns of wire as coil B. If a magnetic field increases with time at the same rate through both coils, which coil (if either) has the larger induced voltage? a. The coil with twice as many turns will have twice the induced voltage. b. The coils will have the same induced voltage since the magnetic field increases at the same rate. c. The coil with half as many turns will have twice the induced voltage.

a. The coil with twice as many turns will have twice the induced voltage.

If the magnetic field produced by the magnets in a generator is constant, does the magnetic flux through the generator coil change when it is turning? Explain. a. Yes, the flux through the coil is continuously changing because the coil is rotating. b. Yes, the flux through the coil is continuously changing because the arc of the coil is changing. c. No, the flux is constant because the magnetic field is constant.

a. Yes, the flux through the coil is continuously changing because the coil is rotating.

A horizontal wire is oriented along a north-south line, and a compass is placed above it. Will the needle of the compass deflect when a current flows through the wire, and if so, in what direction? a. Yes, the needle will deflect away from north. b. Yes, the needle will deflect directly south. c. Yes, the needle will deflect directly east. d. No, the needle will not deflect.

a. Yes, the needle will deflect away from north.

If we look down at the top of a circular loop of wire whose plane is horizontal and that carries a current in the clockwise direction, what is the direction of the magnetic field at the center of the circle? a. perpendicular to the loop and down at the center b. no magnetic field c. perpendicular to the loop and up at the center d. clockwise e. counterclockwise

a. perpendicular to the loop and down at the center

A transformer has 20 turns of wire in its primary coil and 75 turns on its secondary coil. (a) Is this a step-up or step-down transformer? a. step-up b. step-down (b) If an alternating voltage with an effective voltage of 140.0 V is applied to the primary, what is the effective voltage induced in the secondary? _____ V

a. step-up b. 525

A positive charge is released from rest near a bar magnet. The magnetic force on the charge a. there is no magnetic force on the charge. b. repels it away from the N pole of the magnet. c. attracts it toward the S pole of the magnet. d. attracts it toward the N pole of the magnet. e. repels it away from the S pole of the magnet.

a. there is no magnetic force on the charge.

Electrons flow around a circular wire loop in a horizontal plane, in a direction that is clockwise when viewed from above. This causes a magnetic field. Inside the loop, the direction of this field is a. up. b. down. c. radially outward from the center of the loop. d. toward the center of the loop.

a. up.

A transformer has 200 turns on the primary and 20 turns on the secondary. The primary is connected to a direct current source of 100 millivolts. The voltage in the secondary coil will be a. zero. b. 20 millivolts. c. 1000 millivolts. d. 4000 millivolts. e. 10 millivolts.

a. zero.

Two current-carrying wires are parallel to one another and separated by 1 cm. If the distance between them is increased to 2 cm the new force will be what factor times the original force? a. 1 b. 1/2 c. 2 d. 1/4 e. 4

b. 1/2

Is it possible for a bar magnet to have just one pole? a. Yes b. No

b. No

By stepping up the voltage of an alternating-current source using a transformer, can we increase the amount of electrical energy drawn from the source? Explain. a. Yes, as the voltage is stepped up, the amount of available energy is also increased. b. No, as the voltage is stepped up, the current is stepped down in proportion. c. There is not enough information to determine whether more energy can be drawn.

b. No, as the voltage is stepped up, the current is stepped down in proportion.

A uniform magnetic field is directed horizontally toward the north, and a positive charge is moving west through this field. Is there a magnetic force on this charge, and if so, in what direction? a. Yes, the magnetic force on the charge is directed upward. b. Yes, the magnetic force on the charge is directed downward. c. Yes, the magnetic force on the charge is directed westward. d. Yes, the magnetic force on the charge is directed eastward. e. No, there is no magnetic force on the charge.

b. Yes, the magnetic force on the charge is directed downward.

The magnetic pole near the Earth's north geographic pole is a a. north magnetic pole. b. south magnetic pole. c. scientists have not determined which one yet.

b. south magnetic pole.

A horizontal loop of wire has a magnetic field passing upward through the plane of the loop. If this magnetic field increases with time, is the direction of the induced current clockwise or counterclockwise (viewed from above) as predicted by Lenz's law? a. The current is induced in a counterclockwise direction. b. There is no current induced in the loop. c. The current is induced in a clockwise direction.

c. The current is induced in a clockwise direction.

The north pole of a hand-held bar magnet is brought near the north pole of a second bar magnet lying on a table. How will the second magnet tend to move? a. The second magnet will be unaffected by the first magnet. b. The second magnet will be attracted by the first magnet. c. The second magnet will be repelled by the first magnet.

c. The second magnet will be repelled by the first magnet.

Two identical coils of wire are placed on a single horizontal wooden broom handle. The coils are separated by a few centimeters. We now run identical currents in the same direction through each coil. The coils experience a. a repulsive magnetic force. b. an attractive electrostatic force because one coil is negatively charged and the other positively charged. c. an attractive magnetic force. d. no forces because the currents are identical. e. a repulsive electrostatic force because both coils are identically charged.

c. an attractive magnetic force.

A horizontal straight wire carries a current from south to north. The resulting magnetic field lines are a. closed circles perpendicular to the wire directed counterclockwise as viewed from the south. b. straight lines perpendicular to the wire. c. closed circles perpendicular to the wire directed clockwise as viewed from the south. d. parallel to the wire from north to south. e. parallel to the wire from south to north.

c. closed circles perpendicular to the wire directed clockwise as viewed from the south.

Imagine that this classroom contains a constant magnetic field that points from the front to the back. In front of you a negative charge is slowly moving horizontally to your left. As you watch, the magnetic force on the charge a. deflects the charge toward you. b. has no effect on the charge. c. deflects the charge into a clockwise directed vertical circle. d. deflects the charge into a counterclockwise vertical circle. e. deflects the charge away from you.

d. deflects the charge into a counterclockwise vertical circle.

If a uniform magnetic field is directed horizontally toward the east, and a negative charge is moving east through this field, is there a magnetic force on this charge, and if so, in what direction? a. Yes, the magnetic force is directed upward. b. Yes, the magnetic force is directed downward. c. Yes, the magnetic force is directed eastward. d. Yes, the magnetic force is directed westward. e. No, there is no magnetic force on the charge.

e. No, there is no magnetic force on the charge.