Chapter 14: Electromagnetism
1. 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. toward the center of the loop.
D. radially outward from the center of the loop.
2. A horizontally moving charge enters a magnetic field that points up. The magnetic force pushes the charge to the right of its original path when viewed from the perspective of the charge. What is the sign of the charge?
A. negative
B. positive
C. Not enough information to answer.
3. Which of these will always produce a magnetic field?
A. a negative charge at rest
B. a positive charge at rest
C. another magnetic field
D. a moving charge
5. When a current is induced by a changing magnetic field B1, the current always produces a second magnetic field B2 such that
A. B1 and B2 combine to give a stronger magnetic field than B1 alone.
B. B1 and B2 combine to give a weaker magnetic field than B1 alone.
C. B1 and B2 completely cancel each other out.
D. It is not possible to tell whether the combined field is stronger or weaker than B1 without more information.
6. A permanent magnet is produced when
A. electrons become stuck and cease to move.
B. magnetic fields of large groups of individual atoms are permanently aligned.
C. current is made to circulate in a clockwise direction in a loop of wire.
D. electrical fields exchange electrons with the magnetic fields.
7. A positive charge is released from rest near a bar magnet. The magnetic force on the charge
A. attracts it toward the N pole of the magnet.
B. attracts it toward the S pole of the magnet.
C. repels it away from the N pole of the magnet.
D. repels it away from the S pole of the magnet.
E. There is no magnetic force on the charge.
8. A bar magnet and an electrically polarized object are placed next to each other on a table. What happens?
A. The positive part of the object turns toward the north pole of the magnet.
B. The positive part of the object turns toward the south pole of the magnet.
C. The object and magnet accelerate toward each other until they touch and then they repel.
D. Nothing happens.
9. A current flowing through a long straight wire causes a magnetic field that points
A. radially outward from the wire.
B. radially inward towards the wire.
C. along the wire.
D. along concentric circles around the wire.
10. A little magnetic compass has a needle whose tips are clearly labeled N and S. The compass is placed next to a single circular loop of wire lying flat on a wooden table. The current in the loop is clockwise. What happens?
A. The N tip of the needle is attracted towards the loop.
B. The S tip of the needle is attracted towards the loop.
C. The needle orients itself with the N tip pointing in the direction of the current in the segment of the loop closest to the needle.
D. The needle orients itself with the S tip pointing in the direction of the current in the segment of the loop closest to the needle.
E. None of these.
11. A magnetic compass points towards the north geographic pole of the Earth because
A. all magnetic poles, north or south, point that way due to the spin of the Earth.
B. there is a north magnetic pole near the north geographic pole.
C. there is a south magnetic pole near the north geographic pole.
D. the static electricity in the atmosphere causes the alignment of the compass.
12. 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. no forces because the currents are identical.
B. an attractive magnetic force.
C. a repulsive magnetic force.
D. an attractive electrostatic force because one coil is negatively charged and the other positively charged.
E. a repulsive electrostatic force because both coils are identically charged.
13. Which of the following cannot induce a voltage in a loop of wire?
A. Expanding or contracting the loop in a region where there is no magnetic field.
B. Moving the loop near a magnet.
C. Moving a magnet near the loop
D. Changing the current in a nearby loop.
27. The correct expression for magnetic flux through area A, where B is the magnetic field and A is an area perpendicular to the field is
A. B ´ A.
B. B + A.
C. B/A.
D. A/B.
E. 1/(B ´ A).
28. Think of a closed rectangular loop of wire around the edge of this page. A magnetic field perpendicular to the page points upward and increases in strength in a certain time. During this time the conventional current induced in the loop will be
A. clockwise.
B. counterclockwise.
C. zero.
D. continually changing direction.
31. The south pole of a bar magnet is moved toward a short helical coil of wire (solenoid) along the axis of the coil. The coil has 100 turns and the ends of the coil are connected to form a closed circuit. If the coil is replaced with a single loop of wire of the same diameter, and the magnet is moved exactly as before, the current induced in the loop is
A. the same as in the coil.
B. 100 times smaller.
C. 100 times larger.
D. zero in both cases.
34. If an electron is placed at rest near a bar magnet, the electron will
A. be attracted to the positive pole of the magnet.
B. move in a circular path around the north pole of the magnet.
C. accelerate away from the negative pole of the magnet.
D. not move at all.
35. A bar magnet is broken in half and the magnetic field around one piece is mapped out. What is wrong with this picture?
A. The field lines are pointing in the wrong direction.
B. There is no south pole.
C. The field lines should converge on the ‘N'.
D. Nothing, this is how the field looks around a broken magnet.
37. A loop of wire is oriented in the magnetic field as shown below (the plane of the loop is perpendicular to the direction of the magnetic field). Which of the following is true?
A. There will be an induced current only if the loop is moved to the right.
B. There will be an induced current only if the loop is moved to the left.
C. There will be an induced current only if the loop is moved upward.
D. There will be an induced current only if the loop is moved downward.
E. There will be an induced current if the loop is moved either up or down.
38. Two particles move into a magnetic field. They enter moving at the same speed and direction. The magnitude of the charge on each is known to be the same. One particle moves to the right and the other to the left upon entering the field, the one on the left moving in a larger circle than the one on the right. From this we can say that
A. the leftward moving particle has more mass and is positively charged.
B. the rightward moving particle has less mass and is positively charged.
C. the rightward moving particle has positive charge but we cannot say anything about its mass.
D. the leftward moving particle has more mass but we can't say anything about its charge.
KEYS
1.A
2.B
3.D
5.D
6.B
7.E
8.D
9.D
10.E
11.C
12.B
13.A
27.A
28.A
31.B
34.D
35.B
37.E
38.D