Question 1

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 curls 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

Accepted Answer

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 leftward moving particle has more mass and its charge is opposite the other particle.
D)   the rightward moving particle has positive charge but we cannot say anything about its mass. C

Question 2

If an electron moves in a magnetic field,

Accepted Answer

A)   it always feels a force.
B)   it only feels a force if its velocity vector is parallel (or antiparallel)  to the direction of the magnetic field.
C)   it only feels a force if its velocity vector is not parallel (or antiparallel)  to the direction of the magnetic field.
D)   it does not feel a force if it is in motion, only if stationary. C

Question 3

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?

Accepted Answer

A)   The S tip of the needle is attracted toward the loop.
B)   The N tip of the needle is attracted toward 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. E

Question 4

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

Accepted Answer

A)   no forces because the currents are identical.
B)   a repulsive magnetic force.
C)   an attractive 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.

Question 5

Imagine a magnetic field pointing into the plane of this page. An electron moves across the paper from left to right. The direction of the magnetic force on the electron will be

Accepted Answer

A)   into the plane of the paper.
B)   out of the plane of the paper.
C)   in the plane of the paper and toward the top of the page.
D)   in the plane of the paper and toward the bottom of the page.
E)   in the plane of the paper and opposite the electron's velocity.

Question 6

When there is a changing magnetic flux through an electric circuit, the direction of the induced current in the circuit is determined by _____________ Law.

Accepted Answer

The answer of When there is a changing magnetic flux...

Question 7

A magnetic compass points towards the north geographic pole of the Earth because

Accepted Answer

A)   all magnetic poles, north or south, point that way due to the spin of the Earth.
B)   the static electricity in the atmosphere causes the alignment of the compass.
C)   there is a north magnetic pole near the north geographic pole.
D)   there is a south magnetic pole near the north geographic pole.

Question 8

The scientist credited with discovering that electric currents produce magnetic fields was

Accepted Answer

A)   Oersted.
B)   Ampere.
C)   Coulomb.
D)   Tesla.
E)   Faraday.

Question 9

A positively charged ping pong ball is sitting stationary on the floor in the center of a room. There is also a constant, uniform magnetic field in the room that points toward the ceiling. If I now start the ball rolling toward the back of the room, the resultant motion of the ball, as observed from the ceiling, will be

Accepted Answer

A)   a diagonal straight line toward the left back corner of the room.
B)   a diagonal straight line toward the right back corner of the room.
C)   a horizontal, clockwise circle.
D)   a horizontal, counterclockwise circle.
E)   a straight line in the original direction of motion.

Question 10

The south pole of a bar magnet is moved toward an aluminum ring, along the axis of the ring. As the magnet approaches, the changing magnetic flux induces an electric current in the ring that, when seen from the bar magnet, corresponds to positive charge carriers flowing

Accepted Answer

A)   clockwise.
B)   counterclockwise.
C)   alternating with a fixed frequency.
D)   alternating with a frequency proportional to a speed of the bar magnet.

Question 11

When a current is induced by a changing magnetic field B1, the current always produces a second magnetic field B2 such that

Accepted Answer

A)   B1 and B2 completely cancel each other out.
B)   B1 and B2 combine to give a stronger magnetic field than B1 alone.
C)   B1 and B2 combine to give a weaker magnetic field than B1 alone.
D)   It is not possible to tell whether the combined field is stronger or weaker than B1 without knowing how B1 is changing.

Question 12

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 the same type of wire, and the magnet is moved exactly as before, the current induced in the loop is

Accepted Answer

A)   the same as in the coil.
B)   zero in both cases.
C)   100 times smaller.
D)   100 times larger.

Question 13

Bar A has one end painted green and the other end red and may or may not be a magnet. A student brings the north pole of a bar magnet M close to the green end of A. He observes that the green end is attracted. He can conclude that

Accepted Answer

A)   A is not a magnet.
B)   A is a magnet and the green end is a north pole.
C)   A is a magnet and the green end is a south pole.
D)   A might be a magnet; this observation does not provide enough information to determine whether or not it is.

Question 14

Which of the following cannot induce a voltage in a loop of wire?

Accepted Answer

A)   Moving a magnet near the loop.
B)   Moving the loop near a magnet.
C)   Expanding or contracting the loop in a region where there is no magnetic field.
D)   Changing the current in a nearby loop.

Question 15

An ideal transformer is used to either increase or decrease the voltage in an AC circuit. When the output voltage is greater than the input voltage of a transformer then

Accepted Answer

A)   the power output depends on the ratio of turns in the primary and secondary.
B)   the power output is the same as the power input.
C)   the power output is larger than the power input.
D)   the power output is smaller than the power input.

Question 16

A bar magnet and an electrically polarized object are placed next to each other on a table. What happens?

Accepted Answer

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.

Question 17

Two long bar magnets are aligned so that north poles face each other. The magnets are separated by 1 cm, and a repulsive force between the north poles is 0.04 N. When the separation is increased to 2 cm the force will be

Accepted Answer

A)   0.010 N.
B)   0.020 N.
C)   0.025 N.
D)   0.40 N.
E)   0.050 N.

Question 18

A positive charge is released from rest near a bar magnet. The magnetic force on the charge

Accepted Answer

A)   There is no magnetic force on the charge.
B)   Either pole of the magnet will repel the positive charge.
C)   can only be attracted toward the S pole of the magnet.
D)   can only be attracted toward the N pole of the magnet.

Question 19

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?

Accepted Answer

A)   There will be an induced current only if the loop is moved to the left.
B)   There will be an induced current only if the loop is moved to the right.
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.

Question 20

In outer space, you observe a straight stream of electrons flowing past you at 14.5 miles per second, about the same speed that Mars moves on its orbit around the sun.  You maneuver your spacecraft to face the current so that the electrons are moving from left to right and so that you are 10 m from the stream. In what direction does a compass needle point?

Accepted Answer

A)   up 
B)   down 
C)   left 
D)   right 
E)   You observe no magnetic field.

Exam 14: Magnets and Electromagnetism