Deck 7: Magnetism and Electromagnetism

Question 1

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

Answer 1

True

Question 2

Two north magnetic poles attract one another.

Answer 2

False

Question 3

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

Answer 3

False

Question 4

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

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

Question 5

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

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

Question 6

Flux lines are concentrated at the center of a magnet.

Question 7

A DC generator produces a smooth DC voltage output.

Question 8

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

Question 9

Magnetic flux is another name for a magnetic field.

Question 10

Aluminum, brass, and iron make good magnets.

Question 11

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

Question 12

The opposition)to being magnetized is called permeability

Question 13

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

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

Question 14

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

Question 15

Unlike magnetic poles repulse one another.

Question 16

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

Question 17

A solenoid converts electrical energy into mechanical energy.

Question 18

Soft iron, copper, and silver make good magnets.

Question 19

A solenoid consists of ________.

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

Question 20

Permeability is ________.

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

Question 21

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 22

Unlike magnetic poles ________ and like poles ________.

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

Question 23

The polarity of an induced voltage depends on the ________.

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

Question 24

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

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

Question 25

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)240
B)0
C)60
D)120

Question 26

If a tape recorderʹs output voltage increases and decreases when you shake the recorder, a possible problem might be ________.

A)too high a sourceVoltage
B)an open circuit in the speaker
C)a loose circular magnet around the speakerʹsV
Oice coil
D)an open capacitor

Question 27

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

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

Question 28

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

Question 29

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

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

Question 30

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

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

Question 31

The permeability of air is ________.

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

Question 32

A weber is a unit of ________.

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

Question 33

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

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

Question 34

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

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

Question 35

A tesla is a unit of ________.

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

Question 36

The magnetic term that is equivalent to voltage is ________.

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

Question 37

The magnetic field around an electromagnet is produced by ________.

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

Question 38

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

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

Question 39

In which one of the following applications is electromagnetism used?

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

Question 40

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

A)remains the same
B)decreases
C)increases

Question 41

Like magnetic poles ________.

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

Question 42

The movable part of the relay is the:

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

Question 43

Soft iron has a high ________.

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

Question 44

An ampere-turn is a unit of ________.

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

Question 45

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 conductor and the magnetic field.
D)motion between the magnetic poles.

Question 46

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

A)remains the same
B)decreases
C)increases

Question 47

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 48

A relay is a device that ________.

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

Question 49

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

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

Question 50

Applying an ac voltage to an electromagnetʹs coil Will produce a ________.

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

Question 51

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

Question 52

The movable part of the solenoid is the:

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

Question 53

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

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

Question 54

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

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

Question 55

A simple electric doorbell probably uses ________ to ring the bell.

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

Question 56

The ________ electromagnet cannot be further magnetized.

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

Question 57

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

A)decrease
B)increase
C)remain the same

Question 58

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

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

Question 59

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

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

Question 60

Reversing the current through an electromagnet ________ the magnetic field.

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

Question 61

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

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

Question 62

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

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

Question 63

Faradayʹs law states that the voltage induced across a coil of Wire is proportional to these two factors.

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

Question 64

Induced voltage resulting from electromagnetic induction is proportional to:

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

Question 65

Faradayʹs law and Lenzʹs law are related in that they deal With:

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

Question 66

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

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