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Elementary Electrical Engineering (AC/DC) > The Nature of Magnetism > Flashcards

The Nature of Magnetism Flashcards

1
Q

The phenomenon of magnetism was discovered by the _____ about _______.

A

Chinese, 2637 B.C.

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2
Q

The magnets used in the primitive compasses were called ________ or _______.

A

lodestones, leading stones

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3
Q

What are the crude pieces of iron ore called lodestones?

A

magnetite

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4
Q

Lodestones are classified as what type of magnets?

A

natural magnets

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5
Q

What is the only other natural magnet aside from lodestones?

A

the earth itself

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6
Q

What are all other magnets made by humans known as?

A

artificial magnets

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7
Q

These are those materials which are attracted or repelled by a magnet and which can be magnetized themselves.

A

magnetic materials

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8
Q

most common magnetic materials

A

iron and steel

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9
Q

those of hard magnetic materials that retain their magnetism when the magnetizing field is removed

A

permanent magnets

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10
Q

one that has no ability to retain a magnetized state when the magnetizing field is removed

A

temporary magnet

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11
Q

Classifications of Magnetic Materials based on applications

A

Ferromagnetic materials, Paramagnetic materials, Diamagnetic materials

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12
Q

Classifications of Magnetic Materials based on strong magnetic properties of iron

A

magnetic, nonmagnetic

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13
Q

includes iron, steel, nickel, cobalt, and commercial alloys

A

ferromagnetic materials

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14
Q

nonmagnetic materials that have ferromagnetic properties of iron

A

ferrites

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15
Q

A common application of a ferrite is a ferrite core in the coils for __________.

A

RF (radio-frequency) transformers

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16
Q

range of permeability of ferrites

A

50 to 3000

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17
Q

includes aluminum, platinum, manganese, and chromium

A

paramagnetic materials

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18
Q

relative permeability of paramagnetic materials

A

slightly more than 1

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19
Q

includes bismuth, antimony, copper, zinc, mercury, gold, and silver

A

diamagnetic materials

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20
Q

relative permeability of diamagnetic materials

A

less than 1

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21
Q

two points of a magnet opposite each other

A

north pole, south pole

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22
Q

force that exists arounds the magnet invisible to the naked eye

A

magnetic field

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23
Q

the ______ the magnet, the greater the number of lines of force and the ________ the area covered by the filed

A

stronger, larger

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24
Q

What does the direction of the lines outside the magnet shows?

A

path a north pole would follow in the field

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25
Q

What do you call an entire group of magnetic field lines which flow outward from the north pole of a magnet?

A

magnetic flux

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26
Q

What is the symbol for magnetic flux?

A

Greek lowercase letter phi

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27
Q

What is the SI unit of magnetic flux?

A

weber (Wb)

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28
Q

1 Weber = n magnetic field lines
n = ?

A

1 x 10^8

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29
Q

What is the symbol for magnetic flux density?

A

B

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30
Q

What is one weber per square meter called?

A

tesla

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31
Q

It is the magnetic flux per unit area of a section perpendicular to the direction of flux.

A

Magnetic Flux Density

32
Q

SI unit of magnetic flux density

A

tesla (T)

33
Q

When was the relation between magnetism and electric current discovered?

A

1819

34
Q

Who discovered that an electric current flowing through a conductor produced a magnetic field around that conductor?

A

Danish scientist Oersted

35
Q

A _____ current will produce many lines of force extending far from the wire, while a _____ current will produce only a few lines close to the wire.

A

high, low

36
Q

Every section of the wire has the field of force around it in a plane _______ to the wire.

A

perpendicular

37
Q

What is a convenient way to determine the relationship between the flow of current in a conductor and the direction of the magnetic lines of force around the conductor?

A

right-hand rule

38
Q

two results of bending a straight conductor into the form of a single loop

A

magnetic fields are denser inside the loop, all lines inside the loop are aiding in the same direction

39
Q

When is a coil of wire conductor formed?

A

more than one loop or turn

40
Q

What is the symbol for magnetomotive force?

A

F

41
Q

SI unit for magnetomotive force

A

ampere-turns (At)

42
Q

The _____ of a magnetic field in a coil of wire depends on how much current flows in the turns of the coil.

A

strength

43
Q

The more current, the ______ the magnetic field.

A

stronger

44
Q

The more turns, the more ______ are the lines of force.

A

concentrated

45
Q

the product of the current times the number of turns of the coil

A

magnetomotive force

46
Q

formula of magnetomotive force

A

F = NI

47
Q

formula of magnetic flux density

A

B = Φ/A

48
Q

concentration of lines of forces; depends on how long the coil is

A

magnetic field intensity

49
Q

If a coil with a certain number of ampere-turns is stretched out to twice its original length, the intensity of the magnetic field will be ________.

A

half as great

50
Q

symbol of magnetic field intensity

A

H

51
Q

formula of magnetic field intensity

A

H = F/l

52
Q

also known as BH curve

A

flux-field curve

53
Q

used to show how much flux density results from increasing the amount of field intensty

A

flux-field curve

54
Q

it is the ratio of flux density to field intensity

A

permeability

55
Q

unit of permeability

A

Tm/At

56
Q

The average value of permeability is measured at the point where the ______ is first established

A

knee

57
Q

permeability of air

A

4π x 10^-7 Tm/At

58
Q

What is the opposition to the production of flux in a material called?

A

reluctance

59
Q

symbol for reluctance

A

R

60
Q

it is inversely proportional to permeability

A

reluctance

61
Q

iron has high permeability and therefore ____ reluctance

A

low

62
Q

air has ______ permeability and hence has high reluctance

A

low

63
Q

formula of reluctance

A

R = l/µA

64
Q

states that if a conductor “cut across” lines of magnetic force, or if lines of force cut across a conductor, an emf or voltage is induced across the ends of the conductor

A

Principle of Electromagnetic Induction

65
Q

When was the principle of electromagnetic conduction discovered and who discovered it?

A

1831, Michael Faraday

66
Q

The most important application of relative motion between conductor and magnetic field is made in _________.

A

electric generators

67
Q

In a DC generator, how are fixed electromagnets arranged?

A

in a cylindrical housing

68
Q

Since the conductors are in series in the coil, the induced voltages add together to produce the _______ of the generator.

A

output voltage

69
Q

According to ________, the value of the induced voltage depends upon the number of turns of a coil and how fast the conductor cuts across the lines of force or flux.

A

Faraday’s Law

70
Q

states that an induced voltage always has such a direction as to oppose the change in magnetic flux that produced it

A

Lenz’s Law

71
Q

Three Factors determining Induced Voltage

A

amount of flux, number of turns, time rate of cutting

72
Q

The more the lines of force that cut across the conductor, the _____ the value of induced voltage.

A

higher

73
Q

The more turns in a coil, the ______ the induced voltage.

A

higher

74
Q

The faster the flux cuts a conductor, or the conductor cuts the flux, the _______ the induced voltage because ______ lines of force cut the conductor within a given period of time.

A

higher, more

75
Q

Formula for Faraday’s Law and Lenz’s Law

A

ε = N(ΔΦ/Δt)

Elementary Electrical Engineering (AC/DC) (9 decks)

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