Magnetism_short answer_multiple choice

Question 1

Lodestone
a. is a type of iron ore
b. can attract small pieces of iron
c. will rest in a north-south direction when allowed to pivot freely
d. has all of the above characteristics
e. has none of the above characteristics

Answer 1

d. has all of the above characteristics

Question 2

The N-pole of a bar magnet will
a. attract a positive charge and repel a negative charge
b. repel a positive charge and attract a negative charge
c. attract positive and negative charges
d. repel positive and negative charges
e. not affect a charged object

Answer 2

e. not affect a charged object

Question 3

Which statement about the magnetic north pole of Earth is true?
a. Its location never changes.
b. It corresponds to the N-pole of a bar magnet.
c. It corresponds to the S-pole of a bar magnet.
d. It is at the same location as the geographic north pole of Earth.
e. both B and D

Answer 3

c. It corresponds to the S-pole of a bar magnet.

Question 4

Magnetic field lines
a. show the strength of a magnetic field
b. show the direction of a magnetic field
c. become more widely spaced as the magnetic force weakens
d. all of the above
e. none of the above

Answer 4

d. all of the above

Question 5

Which statement about magnetic fields is NOT true?
a. The spacing of the field lines indicates the strength of the field.
b. There is no magnetic field inside a magnet.
c. Field lines do not cross one another.
d. The field is three-dimensional.
e. The field weakens as the distance from the magnet increases.

Answer 5

b. There is no magnetic field inside a magnet.

Question 6

Two equal bar magnets are placed end-to-end with opposite poles a small distance apart. If a small piece of iron is placed exactly halfway between the magnets, the iron will

Answer 6

c. stay in the middle

Question 7

A magnetic domain is best described as
a. the magnetic field around a magnet
b. an atom that acts as a tiny magnet
c. a group of atoms with their magnetic axes lined up in the same direction
d. a metal that can be magnetized by induction
e. the strength of a magnetic field

Answer 7

c. a group of atoms with their magnetic axes lined up in the same direction

Question 8

The field lines around a straight conductor are drawn in clockwise circles around the conductor. The current in the conductor must be travelling

Answer 8

a. into the page

Question 9

Two separate wires are placed side by side. When a current travels through them, they repel one another.
Which statement best explains this observation?
a. The wires have magnetic fields around them.
b. The currents are flowing in opposite directions.
c. Both currents are flowing in the same direction.
d. both A and C
e. both A and B

Answer 9

e. both A and B

Question 10

The strength of the magnetic field of a coil may be increased by
a. increasing the current in the wire
b. wrapping it around an iron core
c. increasing the number of loops in the coil
d. all of the above
e. none of the above

Answer 10

d. all of the above

Question 11

Which of the following changes would cause the armature of a DC motor to turn faster?
a. increasing the current in the circuit
b. increasing the number of turns in the coil
c. increasing the strength of the field magnets
d. all of the above
e. none of the above

Answer 11

d. all of the above

Question 12

The brushes of a DC motor
a. connect the coil to the armature
b. provide a permanent magnetic field
c. allow the armature to spin easily
d. connect the coil to the circuit
e. change direction with every rotation of the armature

Answer 12

d. connect the coil to the circuit

Question 13

If the split-ring commutator of a DC motor was replaced with a solid commutator ring, the armature would
a. rotate more quickly
b. rotate in the opposite direction
c. stop when the coil was at right angles to the magnetic field
d. stop when the coil was parallel to the magnetic field
e. rotate more slowly

Answer 13

c. stop when the coil was at right angles to the magnetic field

Question 14

A current can be induced in a straight conductor when

Answer 14

d. The conductor is held in a changing magnetic field.

Question 15

Which of the following factors does not affect the size of the induced current in a coil?
a. number of turns in the coil
d. size of the inducing field
b. rate of change of the inducing field
e. direction of the windings in the coil
c. resistance of the wire in the coil

Answer 15

e. direction of the windings in the coil

Question 16

A coil is connected to a galvanometer. When a permanent magnet is held steady in the center of the coil, the galvanometer will indicate

Answer 16

no current

Question 17

Which of these factors would increase the output of a generator?
a. increasing the rate of rotation of the armature
b. increasing the strength of the field magnets
c. increasing the number of coils on the armature
d. all of the above
e. none of the above

Answer 17

d. all of the above

Question 18

If the connections to a step-up transformer are reversed and the secondary coil is now the primary coil, what will be the result?

Answer 18

c. The transformer will step down the potential difference.

Question 19

A step-down transformer changes

Answer 19

High potential difference to low potential difference.

Question 20

The advantage of AC power over DC power is that

Answer 20

a. AC power allows the operation of transformers.

Question 21

metal ring split into two parts

Answer 21

commutator

Question 22

53. Do magnetic field lines have a beginning and an end?

Answer 22

No, the field lines are closed loops.

Question 23

54. A commercial advertises a “magnetic” glove that you can wear to dust furniture. It is made of a soft cloth. The glove actually does attract dust. How does it work?

Answer 23

It’s not really magnetic. The glove attracts dust using electrostatic forces, not magnetic forces.

Question 24

56. How are magnetic poles similar to electric charges? How are they different?

Answer 24

Magnetic poles are similar to electric charges because they can each be positive or negative (2 types), produce three-dimensional force fields between them, produce fields with a direction, and can produce both repulsive and attractive forces. They are different because electric charges can be isolated; magnetic poles cannot be isolated

Question 25

58. Explain what happens when you break a bar magnet in half and why.

Answer 25

When you break a bar magnet in half you get 2 smaller bar magnets, each with 2 opposite poles. The original poles of the magnet remain the same, the ones that are broken are the opposite of the originals.

Question 26

59. Two bar magnets are made of the same type of iron; however, one is much stronger than the other. How can this happen?

Answer 26

The stronger has more domains that are aligned with the same polarity, if the particles are more aligned the magnet will be stronger. The weaker one’s domain is less aligned, more random directions.

Question 27

60. Bank cards and audiotapes often become useless after exposure to a strong magnetic fields. Suggest reasons why this happens.

Answer 27

This happens because the domains of the magnets (in both objects that store information in the magnets) are rearranged by the exposure to a strong magnetic field.

Question 28

A lifting electromagnet is often made in a U-shape, with two separate coils making up the legs of the U. If the electromagnet is to be used to lift scrap iron, would it be better to have similar poles at the bottom of the legs, or dissimilar poles ?

Answer 28

It would be better to have opposite poles on the ends. The magnetic field could travel from one pole, through the scrap metal, to the other pole. This would increase the lifting ability of the electromagnet. If the poles were similar, the field lines would not be continuous.

Question 29

65. A student has used up all of the available wire to make an electromagnet. Describe two ways the student could still increase the strength of the electromagnet.

Answer 29

Tighten the loops, to create more (smaller radius means more loops). And increase the current flowing through the wire.

Question 30

67. In which direction can an electric charge move in an magnetic field, without having a force exerted on it?

Answer 30

It can move parallel to the magnetic field (follow the path).

Question 31

70. A galvanometer is connected to a coil. Describe the readings on the galvanometer when a bar magnet is plunged into the coil, held steady, and then removed.

Answer 31

The readings would increase (indicate a current) as it is plunged in, go to zero when held steady, and increase (indicating a current, in the opposite direction to the first) when removed.

Question 32

71. What is the difference between alternating current and direct current?

Answer 32

Direct current always moves in the same direction, alternating current can change direction at certain intervals

Question 33

72. Why doesn't the armature of a DC generator stop when the split in the commutator ring allows no contact with the brushes?

Answer 33

Due to the inertia of the armature, it continues to move in the direction it was heading, then reinforced when it connects again.

Question 34

73. What happens when the connections to a step-down transformer are reversed?

Answer 34

It becomes a step-up transformer.

Question 35

74. If you are building a transformer and you want a lower potential difference in the secondary coil than in the primary, should the secondary coil have fewer loops or more loops?

Answer 35

fewer

Question 36

75. Describe three devices or methods that could be used to turn the turbine of a generator, allowing it to produce electricity.

Answer 36

Wind with a windmill, water with a water wheel, or a hand cranking a hand crank.

Question 37

76. The electrons in the current produced at a generating station never actually reach your home. How is it possible for electricity to be transmitted?

Answer 37

Electrons are not transferred, only the energy is. The electrons in an AC current reverse direction continuously—they do not leave the circuit. Transformers along the way induce currents in separate circuit—electrons do not move from one circuit to another