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Magnetism > Self tests 1-3 > Flashcards

Self tests 1-3 Flashcards

1
Q

What is another name for magnetic lines of force?

A

magnetic flux

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2
Q

why don’t magnetic lines of force collapse into the centre of a magnet?

A

the magnetic lines of force do not collapse due to mutual repulsion

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3
Q

T/F? Magnetic lines of force never cross

A

True

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4
Q

T/F? Magnetic lines of force start at the north pole and end at the south pole

A

False

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5
Q

T/F? It is not possible to have a north pole without having an accompanying south pole

A

True

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6
Q

T/F? The north pole of the earth is actually a south magnetic pole

A

True

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7
Q

T/F? The arrows on the magnetic lines of force always point from north to south outside of the magnet, and south to north on the inside of the magnet

A

True

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8
Q

T/F? Unlike poles of magnets repel each other

A

False

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9
Q

T/F? Magnetic screens are made of materials with a low reluctance

A

True

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10
Q

T/F? Magnetic screens block magnetic flux lines

A

False

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11
Q

List three ways of creating magnets?

A
  • using electrical current
  • stroking with a magnet
  • by linking with another magnetic field and tapping
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12
Q

List three ways of demagnetizing a material?

A
  • Using heat
  • AC current
  • tapping or vibrating excessively
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13
Q

Which method of demagnetizing is commonly used by watchmakers?

A

AC current method

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14
Q

What is meant by the term “curie” temperature?

A

temperature at which the molecular structure changes

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15
Q

When a piece of ferromagnetic material is brought near a magnet, the ferromagnetic material becomes magnetized. This process is referred to as ?

A

Magnetic induction

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16
Q

Is it true that any time a charge moves, there must be a magnetic field set up around that charge?

A

Yes

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17
Q

why are there no magnetic poles in the field surroundings current-carrying conductor?

A

there is no magnetic material

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18
Q

As the direction of current in a conductor is reversed, what happens to compasses surrounding the conductors?

A

the compass also reverses direction

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19
Q

As the current in a conductor is increased, what happens to the magnetic lines of force surrounding the conductor?

A

More flux lines are made and forced outwards

20
Q

When current remains steady, does the field disappear?

A

No it remains steady

21
Q

Is the field around the conductor more or less dense closer to the conductor?

A

more dense

22
Q

As the current in a conductor is decreased, what happens to the magnetic lines of force surrounding the conductor?

A

They collapse inward

23
Q

I’m moving four times as far away from a current-carrying conductor, the density of the flux lines will have ____________ by ____________ times?

A

decreased by four

24
Q

Parallel conductor carrying currents in the same direction _________ each other and parallel conductors carrying currents in the opposite directions ___________ each other?

A

attract , repel

25
Q

Using the left hand rule for coils, the thumb points in the direction of?

A

North pole of coil

26
Q

four things that affect the strength of an electromagnetic coil?

A
  • number of turns
  • core material
  • spacing between
  • vary current through the coil
27
Q

Materials that act in a similar way to iron in a magnetic field are referred to as?

A

ferromagnetic

28
Q

Two examples of non-magnetic material?

A

air, wood

29
Q

Most practical way of varying the strength of an electromagnet?

A

vary the current through the coil

30
Q

What device connected in series with the electromagnet is normally used to do this?

A

rheostat

31
Q

why must electrical bus bars be securely braced?

A

Because strong magnetic forces occur between bus bars if there is a short

32
Q

In the dot-and-cross convention used to indicate the direction of current flow a ___________ represents a current coming out of the page at you?

A

dot

33
Q

The magnetic flux in a circuit is directly proportional to the ___________ and inversely proportional to the ___________ of the magnetic circuit?

A

Magnemotive force, reluctance

34
Q

Opposition to the formation of flux lines in magnetic circuit is called?

A

Reluctance

35
Q

The point at which all of the domains in the magnetic material have aligned themselves with the magnetic field is referred to as?

A

theoretical saturation

36
Q

Residual magnetism is a measure of the amount of __________ remaining in the magnetic material after the magnetizing force has been removed?

A

flux density

37
Q

The amount of reverse magnetizing force required to remove the residual magnetism is called the?

A

coercive force

38
Q

The type of core material used for lifting electromagnets would have a ___________ retentivity.

A

low

39
Q

The spreading out of the flux lines in an air gap is referred to as _____

A

fringing

40
Q

Magnetic cores that are constructed of alternating layers of magnetic material and electrical insulator are said to be ____________

A

laminated

41
Q

As the reluctance of a magnetic circuit is increased, the flux density of the circuit is ___________?

A

decreased

42
Q

if the magnemotive force applied to a magnetic circuit is increased, the flux density of the circuit is __________?

A

increased

43
Q

The ease with which flux is set up in a unit length and cross-section of a material is referred to as the _________?

A

permeability

44
Q

The term for the lag of flux density behind magnetizing intensity is __________?

A

hysteresis

45
Q

Magnetic cores are usually constructed from materials with a high ___________ and a low ___________ ?

A

permeability, reluctance

46
Q

The amount of energy lost due to the constant reversals of the magnetic field in AC circuits is referred to as ____________ loss

A

hysteresis

47
Q

What form does this energy loss normally take?

A

Heat

Magnetism (7 decks)

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