Deck 11: Magnetism and Electromagnetic Induction

Question 1

An iron rod becomes magnetic when

A) its electrons stop moving and point in the same direction.
B) positive ions accumulate at one end and negative ions at the other end.
C) its atoms are aligned having plus charges on one side and negative charges on the other.
D) the net spins of its electrons are in the same direction.
E) none of these

Answer 1

the net spins of its electrons are in the same direction.

Question 2

Magnetic field lines about a current-carrying wire

A) extend radially from the wire.
B) circle the wire in closed loops.
C) Choices A and B are both correct.
D) None of the above choices are correct.

Answer 2

circle the wire in closed loops.

Question 3

Outside a magnet, magnetic field lines are conventionally drawn from

A) south to north.
B) north to south.
C) either way

Answer 3

north to south.

Question 4

Which pole of a compass needle points to a south pole of a magnet?

A) north pole
B) south pole
C) both of these

Question 5

Transformers use ac so there will be the required

A) magnetic field intensities.
B) voltage for transformation.
C) change in magnetic field for operation.
D) transfer of energy from coil to coil.
E) change in input current.

Question 6

Neon signs require about 12,000 volts to operate. If the circuit uses a 120-volt power source, the ratio of primary to secondary turns on the transformer should be

A) 100:1.
B) 1:100.
C) neither of these

Question 7

If we think of the Earth as a magnet, its north (-seeking) pole is nearest

A) Australia.
B) the Hudson Bay region of Canada.
C) both of these

Question 8

Rapid change of a magnetic field induces

A) an electric field.
B) a magnetic field of the same magnitude.
C) a magnetic field of greater magnitude.

Question 9

A step-up transformer increases

A) power.
B) energy.
C) both power and energy.
D) neither power or energy.

Question 10

Compared to the huge force that attracts an iron tack to a strong magnet, the force that the tack exerts on the magnet is

A) relatively small.
B) equally huge.
C) More information is needed.

Question 11

Voltage can be induced in a wire by

A) changing the current in a nearby wire.
B) moving a magnet near the wire.
C) moving the wire near a magnet.
D) Choices A, B, and C are all true.
E) None of the above choices are true.

Question 12

If the voltage produced by a generator alternates, it does so because

A) the current it produces alternates.
B) alterations in the mechanical energy input.
C) in effect it is an ac motor in reverse.
D) the changing magnetic field that produces it alternates.
E) unlike a battery, it produces alternating current.

Question 13

If a compass is moved from the northern hemisphere to the southern hemisphere, its magnetic needle will change direction

A) hardly at all.
B) by 90 degrees.
C) depending on where the measurement is taken.
D) by 180 degrees.
E) none of these

Question 14

Like kinds of magnetic poles repel while unlike kinds of magnetic poles

A) repel also.
B) may attract or repel.
C) attract.

Question 15

The source of all magnetism is

A) tiny domains of aligned atoms.
B) moving electric charge.
C) ferromagnetic materials.
D) tiny pieces of iron.
E) none of these

Question 16

Metal detectors, like the ones used at airports, are activated by

A) magnetic fields.
B) alternating current.
C) electromagnetic induction.
D) electric fields.

Question 17

Which force field can accelerate an electron, but never change its speed?

A) magnetic field
B) electric field
C) both of these
D) none of these

Question 18

The magnetic field strength inside a current-carrying coil will be greater if the coil encloses a

A) rod of iron.
B) vacuum.
C) glass rod.
D) wooden rod.
E) none of these

Question 19

The intensity of cosmic rays bombarding the Earth's surface is largest at the

A) equator.
B) mid-latitudes.
C) poles.

Question 20

Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a

A) south pole.
B) north pole.
C) north or south pole - no difference really.

Question 21

Compared to the primary voltage, the secondary voltage may be

A) larger.
B) the same.
C) smaller.
D) the same or smaller, but not larger.
E) larger, smaller, or the same.

Question 22

The metal detectors that people walk through at airports operate via

A) Ohm's law.
B) Faraday's law.
C) Newton's laws.
D) civil laws.
E) Coulomb's law.

Question 23

The major advantage of MHD generators over conventional generators is that MHD generators

A) do not require magnets.
B) do not use electromagnetic induction.
C) require no power input.
D) all of these
E) none of these

Question 24

An electron is shot through a spot somewhere between the ends of a horseshoe magnet. The electron

A) is repelled by both poles, and therefore is turned back.
B) is attracted to one of the poles, and repelled by the other.
C) is unaffected by the field.
D) speed is increased.
E) direction is changed.

Question 25

Superconducting electromagnets

A) may be possible in the distant future.
B) may be possible in the near future.
C) exist now.
D) are science fiction.

Question 26

As a motor armature turns faster and faster, net current in the motor windings

A) increases.
B) decreases.
C) remains unchanged.

Question 27

Moving electric charges will interact with

A) only an electric field.
B) only a magnetic field.
C) an electric field or a magnetic field.
D) none of these

Question 28

Magnetic compasses apparently were first used by

A) Greeks.
B) Australian aborigines.
C) Columbus.
D) Vikings.
E) pigeons, then Chinese.

Question 29

Magnetism is due to the motion of electrons as they

A) spin on their axes.
B) move around the nucleus.
C) Choices A and B are both correct.
D) None of the above choices are correct.

Question 30

The principal advantage of ac power over dc power is that

A) more energy is dissipated during transmission.
B) ac circuits multiply power more easily.
C) ac circuits are safer.
D) ac voltage oscillates while dc voltage does not.
E) ac voltage can be transformed via conventional transformers.

Question 31

An electric motor is very similar to

A) an electric generator.
B) a radio receiver.
C) an automobile battery.
D) None of the above choices are correct.

Question 32

If a steady magnetic field exerts a force on a moving charge, that force is directed

A) opposite the direction of the field.
B) in the direction of the field.
C) at right angles to the direction of the field.

Question 33

The output power of an ideal transformer is

A) equal to the input power.
B) smaller than the input power.
C) greater than the input power.
D) may be any of these

Question 34

Electric power can be transmitted from one place to another without the need for connecting wires in between. This statement is

A) sometimes true.
B) always true.
C) always false.

Question 35

Disconnect a small-voltage battery from a coil of many loops of wire and a large voltage is produced by

A) electrons already in the wire.
B) the sudden collapse in the magnetic field.
C) the electric field between the battery terminals.
D) latent energy in the battery.
E) the resistance of the battery to a change in polarity.

Question 36

When a bar magnet is broken in two, each half is

A) at most half as strong as the original magnet.
B) as magnetic as the original magnet.
C) actually stronger than the original magnet.
D) no longer magnetic.

Question 37

the field surrounding every moving electron is

A) always both electric and magnetic.
B) sometimes magnetic and sometimes electric.
C) always magnetic but never electric
D) always electric but never magnetic.
E) none of the above

Question 38

Four amperes of current exist in the primary coil of a transformer. The voltage across the primary coil is 110 V. What is the power output of the secondary coil?

A) 110 W
B) 880 W
C) 27.5 W
D) 440 W
E) not enough information to say

Question 39

A principle difference between an MHD generator and a conventional generator is that the MHD generator

A) has no moving parts.
B) operates more efficiently at high temperatures.
C) Choices A and B are both true.
D) Choices A and B are both false.

Question 40

The voltage across the input terminals of a transformer is 110 V. The primary has 50 loops and the secondary has 25 loops. The voltage the transformer puts out is

A) 25 V.
B) 110 V.
C) 55 V.
D) 220 V.
E) none of these

Question 41

If a steady magnetic field exerts a force on a moving charge, that force is directed

A) in the direction of the motion.
B) opposite the motion.
C) at right angles to the direction of the motion.

Question 42

A certain transformer doubles input voltage. If the primary coil has 10 A of current, then the current in the secondary coil is

A) 10 A.
B) 2 A.
C) 5 A.
D) 25 A.
E) none of these

Question 43

An iron nail is more strongly attracted to the

A) south pole of a magnet.
B) north pole of a magnet.
C) north or south pole - no difference really.

Question 44

Thrust a magnet into a coil of wire and the coil

A) has a current in it.
B) becomes an electromagnet.
C) both of these
D) neither of these

Question 45

If the primary of a transformer were connected to a dc power source, the transformer would have a voltage output

A) at a higher efficiency than with an ac source.
B) that is also dc.
C) only while being connected or disconnected.
D) the same.
E) none of these

Question 46

Which force field can increase a moving electron's speed?

A) only a magnetic field
B) only an electric field
C) either an electric or magnetic field
D) none of these

Question 47

A transformer actually transforms

A) voltage.
B) generators into motors.
C) magnetic field lines.
D) non-safe forms of energy to safe forms of energy.
E) All of the above choices are correct.

Question 48

Pigeons navigate primarily by

A) magnetic sensors in their heads.
B) a good memory.
C) a keen sense of smell.
D) ultra-high-pitched sounds.
E) none of these

Question 49

When a bar magnet is thrust into a coil of copper wire, the coil tends to

A) attract the magnet as it enters.
B) repel the magnet as it enters.
C) both of these
D) neither of these

Question 50

Disregarding the effects of friction, a cyclist will coast farther when a lamp powered by a wheel generator is

A) burned out.
B) of high wattage.
C) of low wattage.
D) none of these

Question 51

When there is a change in the magnetic field in a closed loop of wire

A) a current is created in the loop of wire.
B) a voltage is induced in the wire.
C) electromagnetic induction occurs.
D) all of these
E) none of these

Question 52

Magnetic domains normally occur in

A) copper.
B) silver.
C) iron.
D) all of these
E) none of these

Question 53

A step-up transformer has a ratio of one to ten. Neglecting slight losses, if 100 W of power go into the primary coil, the power coming from the secondary coil is

A) 10 W.
B) 1 W.
C) 100 W.
D) 1000 W.
E) none of these

Question 54

The primary of a transformer is the coil connected to

A) the load.
B) the power line.
C) the Internet.
D) none of these

Question 55

Electromagnetic induction occurs in a coil when there is a change in

A) electromagnetic polarity.
B) voltage in the coil.
C) the coil's polarity.
D) electric field intensity in the coil.
E) magnetic field intensity in the coil.

Question 56

A device that transforms mechanical energy into electrical energy is a

A) magnet.
B) generator.
C) motor.
D) transformer.
E) none of these

Question 57

Magnet A has twice the magnetic field strength of Magnet B and at a certain distance pulls on magnet B with a force of 100 N. The amount of force that magnet A exerts on magnet B is

A) at or about 50 N.
B) exactly 100 N.
C) More information is needed.

Question 58

The force on an electron moving in a magnetic field will be the largest when its direction is

A) at an angle other than 90 degrees to the magnetic field direction.
B) the same as the magnetic field direction.
C) perpendicular to the magnetic field direction.
D) exactly opposite to the magnetic field direction.
E) none of these

Question 59

A wire moving at right angles to a magnetic field has NO induced voltage

A) if it is moving very fast.
B) if it is moving slowly.
C) if the wire is covered with insulation.
D) if it is made of copper.
E) None of the above choices are correct.

Question 60

A device that transforms electrical energy to mechanical energy is a

A) transformer.
B) magnet.
C) generator.
D) motor.
E) none of these

Question 61

If a magnet is pushed into a coil, voltage is induced across the coil. If the same magnet is pushed into a coil with twice the number of loops,

A) the same voltage is induced.
B) twice as much voltage is induced.
C) four times as much voltage is induced.
D) one half as much voltage is induced.
E) none of these

Question 62

A possible cause for the existence of the Earth's magnetic field is due to

A) great numbers of very slow moving charges in the Earth, but not choice A or C.
B) convection currents in the liquid part of the Earth's core, but not choice A or B.
C) moving charges in the liquid part of the Earth's core, but not choice B or C.
D) Choices A, B, and C are all false.

Question 63

Power is transmitted at high voltages because the corresponding current in the wires is

A) low so that overheating of the wires is minimized.
B) also high to deliver appreciable power to distant places.
C) Choices A and B are both true.
D) Choices A and B are both false..