Deck 7: Magnetism and Electromagnetism

Question 1

Soft iron, copper, and silver make good magnets.

Answer 1

False

Question 2

Aluminum, brass, and iron make good magnets.

Answer 2

False

Question 3

Flux lines are concentrated at the center of a magnet.

Answer 3

False

Question 4

A solenoid converts electrical energy into mechanical energy.

Question 5

The left -hand rule can be used to determine the amount of magnetomotive force.

Question 6

Two north magnetic poles attract one another.

Question 7

A DC generator produces a smooth DC voltage output.

Question 8

How does the magnetic field change around a conducting wire if the current increases?

A)It is impossible to predict.
B)The field grows stronger.
C)The field grows weaker.
D)There is no magnetic field around a conducting wire.

Question 9

A strong magnetic field around a conductor indicates a small current flowing through the conductor.

Question 10

A coil of wire with current flowing through it is called a(n).

A)electromagnet
B)south pole
C)north pole
D)capacitor

Question 11

Magnetic flux is another name for a magnetic field.

Question 12

The opposition to being magnetized is called permeability.

Question 13

A solenoid consists of .

A)a burglar alarm relay
B)two plates separated by an insulator
C)a permanent magnet
D)a coil of wire wound around a core

Question 14

A permanent magnet will retain its magnetism for a long period of time.

Question 15

A conductor with no current through it will still have a magnetic field around it.

Question 16

A magnetic field around a conductor is a good indication that current is flowing.

Question 17

Unlike magnetic poles repulse one another.

Question 18

The speed of movement of the coil of a generator affects the direction of current produced.

Question 19

If two north magnetic poles are brought close to each other, .

A)a current is induced
B)a force of attraction pulls them together
C)a force of repulsion pushes them apart
D)an electromagnet is created

Question 20

Permeability is _.

A)the ease of a material to be magnetized
B)the ability of a magnetic material to conduct a current
C)the opposition to being magnetized
D)the shielding effect of a material

Question 21

The permeability of air is .

A)22
B)7
C)19.2
D)1

Question 22

In which one of the following applications is electromagnetism used?

A)loudspeakers
B)relays
C)tape recorders
D)all of these

Question 23

The magnetic term that is equivalent to voltage is .

A)magnetomotive force
B)current
C)flux density
D)reluctance

Question 24

The magnetic field around an electromagnet is produced by .

A)the laminated iron core
B)a current flowing through the winding
C)the conductor's permeability
D)a permanent magnet

Question 25

The quantity of lines of force per unit of area is known as .

A)ampere -turns
B)magnetic flux
C)permeability
D)flux density

Question 26

If a basic one -loop, dc generator rotates at 60 revolutions each second, how many times each second does its dc output voltage reach a peak value?

A)0
B)120
C)240
D)60

Question 27

If a tape recorder's output voltage increases and decreases when you shake the recorder, a possible problem might be _.

A)too high a source voltage
B)a loose circular magnet around the speaker's voice coil
C)an open circuit in the speaker
D)an open capacitor

Question 28

If a relay picks up and makes a contact but does not stay picked up, what's the trouble?

A)The relay coil is open.
B)The magnetic field is too weak.
C)The magnetic field is too strong.
D)There is no trouble. The relay is operating normally.

Question 29

If the cross -sectional area of a magnetic field decreases, the flux density .

A)remains the same
B)increases
C)decreases

Question 30

The polarity of an induced voltage depends on the _.

A)time that the conductor remains stationary in a magnetic field
B)direction of motion of a conductor in a magnetic field
C)amount of current flowing
D)length of a conductor in a magnetic field

Question 31

Which one of the statements below does NOT apply to the voltage induced into a wire when it is moved through a magnetic field?

A)It depends on the length of moving wire in the field.
B)It depends on the current flowing in the wire.
C)It depends on the speed of wire motion.
D)It depends on the strength of the magnetic field.

Question 32

A tesla is a unit of .

A)reluctance
B)magnetic flux density
C)magnetomotive force
D)permeability

Question 33

Unlike magnetic poles and like poles .

A)attract, repel
B)repel, repel
C)attract, attract
D)repel, attract

Question 34

Proximity detectors ususally use a switch in conjunction with a magnet.

A)reed
B)normally closed
C)optical
D)solenoid

Question 35

A weber is a unit of .

A)permeability
B)magnetomotive force
C)reluctance
D)magnetic flux

Question 36

The voltage produced by a magnetic field cutting through a conductor depends on the .

A)speed of motion
B)length of the conductor
C)direction of motion
D)all of the above

Question 37

How will two permanent bar magnets react if they are brought close to each other?

A)They will attract if their north poles are together.
B)They will repel if the north and south poles are together.
C)They will attract if their south poles are together.
D)They will attract if the north and south poles are together.

Question 38

A is a type of electromagnetic device that has a movable iron core called a plunger.

A)analog meter
B)relay
C)solenoid
D)speaker

Question 39

According to the left -hand rule for the magnetic field around a conductor, what points in the direction of current flow?

A)meter
B)index finger
C)thumb
D)fingers

Question 40

If the contacts fail to open when a relay is de -energized, what is the trouble?

A)Dirt is causing the relay armature to stick.
B)There is too little current in the relay coil.
C)The return spring tension is too large.
D)There is no trouble. The relay is operating normally.

Question 41

Applying an ac voltage to an electromagnet's coil will produce a .

A)south magnetic field
B)changing magnetic field
C)north magnetic field
D)steady magnet field

Question 42

The term reluctance in magnetic circuits is like the term in electrical circuits.

A)current
B)resistance
C)voltage
D)capacitance

Question 43

If some turns of wire are removed from an electromagnet, the magnetic field will .

A)be more than the original electromagnet
B)be the same as the original electromagnet
C)be less than the original electromagnet

Question 44

Soft iron has a high .

A)permeability
B)reactance
C)resistance
D)mmf

Question 45

The amount of voltage that is induced in a conductor depends on the .

A)direction of the current flowing
B)direction of motion of the conductor in the magnetic field
C)length of the conductor in the magnetic field
D)length of time a conductor remains stationary in the magnetic field

Question 46

Reversing the current through an electromagnet the magnetic field.

A)reverses
B)decreases
C)collapses
D)increases

Question 47

If more turns of wire are added to a coil and then that coil is moved through a magnetic field, the voltage produced will _.

A)be less than the original coil
B)be the same as the original coil
C)be more than the original coil

Question 48

An iron core electromagnet has a higher than an air core electromagnet.

A)current
B)resistance
C)permeability
D)reactance

Question 49

The movable part of the relay is the:

A)the armature.
B)electromagnetic coil.
C)magnetic field.
D)all of these.

Question 50

If the number of turns of wire on an electromagnet increases, the magnetomotive force mmf .

A)remains the same
B)increases
C)decreases

Question 51

The principal difference between a solenoid and a relay is that:

A)relays relay electricity, solenoids do not.
B)solenoids do electrical work, relays do mechanical work.
C)solenoids do mechanical work, relays do electrical work.
D)relays use magnets, solenoids do not.

Question 52

Increasing the speed at which a magnet moves through a coil of wire causes the induced voltage to .

A)remain the same
B)increase
C)decrease

Question 53

Magnetic lines that are close to each other are said to have a high .

A)reluctance
B)inductance
C)current
D)flux density

Question 54

A simple electric doorbell probably uses to ring the bell.

A)an electromagnet
B)transistor
C)a permanent magnet
D)a DPDT switch

Question 55

Like magnetic poles .

A)have no effect on each other
B)attract each other
C)repel each other
D)have the same current through them

Question 56

A relay is a device that .

A)has a coil to actuate some contacts that control other circuits
B)isolates the actuating signal from the control signal
C)uses an electromagnet to open and close contacts
D)all of these

Question 57

The movable part of the solenoid is the:

A)the plunger.
B)electromagnetic coil.
C)magnetic field.
D)all of these.

Question 58

Hysteresis is a characteristic of magnetic materials wherein a change in magnetization:

A)occurs exactly with the application of a magnetic force.
B)occurs before the application of a magnetizing force.
C)occurs after the application of a magnetic force.
D)varies according to the current flow.

Question 59

The electromagnet cannot be further magnetized.

A)open
B)capacitive
C)saturated
D)shorted

Question 60

An ampere -turn is a unit of .

A)magnetomotive force (mmf)
B)resistance
C)permeability
D)reactance

Question 61

Faraday's law and Lenz's law are related in that they deal with:

A)a resulting current flow.
B)varying magnetic field.
C)an induced voltage.
D)all of these.

Question 62

If a higher voltage is needed from a generator, what must be done?

A)Decrease the number of coils.
B)Turn the coil faster.
C)Increase the distance between the coil and magnetic field.
D)both B and C.

Question 63

When controlling the direction of a dc motor, which winding(s)have their polarity reversed?

A)only the armature
B)either the stator or the armature
C)both the stator and the armature
D)only the stator

Question 64

Induced voltage resulting from electromagnetic induction is proportional to:

A)the number of turns of wire in the coil.
B)the angle at which the conductor cuts the magnetic field.
C)the rate at which the conductor and magnetic fields move relative to each other.
D)all of these.

Question 65

The purpose of a commutator in a dc generator is to:

A)keep current flowing in one direction.
B)maximize the current generated.
C)provide filtration.
D)concentrate flux density.

Question 66

Faraday's law states that the voltage induced across a coil of wire is proportional to these two factors.

A)the size of the magnets and the rate of change of the magnetic flux
B)the number of turns in the coil and the rate of change of the magnetic flux
C)the diameter of the conductor and the rate of change of the magnetic flux
D)the size of the coil and the rate of change of the magnetic flux

Question 67

For a high current switching application where it is not practical to route heavy wiring to the switch location which device would be used?

A)relay
B)electromagnet
C)solenoid
D)generator

Question 68

Electromagnetic induction is best defined as the process by which a voltage is produced in a conductor when there is:

A)energy produced by the rotating coils.
B)motion around the magnetic fields.
C)motion between the magnetic poles.
D)motion between the conductor and the magnetic field.

Question 69

Why is a vibrating wire strain gage appropriate for damp environments?

A)strain is not affected by humidity
B)frequency is not affected by humidity
C)it is a sealed unit
D)all of the above