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SEP Physics Weydon > P7 Magnetism > Flashcards

P7 Magnetism Flashcards

1
Q

Where are magnets strongest

A

At the poles of a magent

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2
Q

Two like poles

A

repel

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3
Q

Opposite poles

A

attract

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4
Q

What does a permanent magnet do

A

Produce its own magnetic field

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5
Q

What does an induced magnet do

A

Become a magnet in a magnetic field

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6
Q

What are the four magnetic metals

A

Iron, Steel, Cobalt, nickel

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7
Q

What is a magnetic field

A

A region around a magnet where a force acts on another magnet or a magnetic material

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8
Q

What happens to a magnetic material when it enters a magnetic field

A

It will experience a force of attraction toward the magnet

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9
Q

What does the strength of an induced magnet depend on

A

The distance from the magnet

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10
Q

What can the direction of a magnetic field be found by

A

Using a compass as it contains a bar magnet

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11
Q

How do you find the magnetic field lines of a magnet

A

Place the south end of a compass on the pole of the magnet, then plot using a cross the direction of the arrow

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12
Q

What direction does a magnet always travel in

A

North to South

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13
Q

How can we tell that the Earth has its own magnetic field

A

A compass points in the North-South direction away from any magnet

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14
Q

What happens when a current flows through a conducting wire

A

A magnetic field is produced around the wire

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15
Q

What does the strength of the magnetic field depend on

A

The size of the current
The distance to the wire

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16
Q

What is a solenoid

A

wire with a number of turns

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17
Q

What type of magnetic field does a solenoid produce

A

A strong and uniform magnetic field when the current is turned on

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18
Q

What shape is the magnetic field around a solenoid similar to

A

The magnetic field of a bar magnet

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19
Q

How do you increase the strength of the magnetic field produced by a solenoid

A

Increase the size of the current
Increase the number of turns of the solenoid
Placing an iron core in the solenoid

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20
Q

What is an electromagnet

A

A solenoid with an iron core

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21
Q

Why are electromagnets useful

A

They can be turned on and off
The strength of the magnetic field can be changed by changing the size of the current

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22
Q

What is a relay used for

A

To turn on and off high voltage appliances

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23
Q

What does a relay contain

A

Two separate circuits

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24
Q

What are the components of a low-voltage circuit in a relay

A

It contains an electromagnet which makes it safe to turn on and off

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25
Q

What are the components of a high-voltage circuit in a relay

A

Two metal contacts are used to replace a switch

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26
Q

What does the contact in a relay connect to

A

A spring that keeps the contacts apart and also an iron core next to it

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27
Q

What happens when the low-voltage circuit in a relay is switched on

A

A current flows around the circuit which produces a magnetic field around the electromagnet

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28
Q

What does the magnetic field in a relay attract to

A

An iron block

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29
Q

What does the iron block in a relay cause

A

The contacts to close and switch on the high voltage circuit

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30
Q

What does a doorbell contain

A

An electromagnet

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31
Q

In a doorbell, what happens when the buzzer is pressed

A

The switch closes which causes a current to flow through the circuit

32
Q

What happens when current flows through the circuit in a doorbell

A

A magnetic field is produced by the electromagnet which causes the iron contact to be attracted toward the magnetic field

33
Q

What happens when the iron core is attracted towards the magnetic field in a doorbell

A

The contact causes the clapper to hit the bell which breaks the circuit so the iron contact returns to its original postition

34
Q

What happens when a magnetic field is placed between a wire

A

The wire interacts with the magnetic field which causes it to experience a force

35
Q

What is magnetic flux density a measure of

A

The strength of the magnetic field

36
Q

What is the motor effect used in

A

Electric motors

37
Q

In a magnetic field, what does a loop of wire experience

A

A force on both the left and right sides

38
Q

What direction does a loop of wire in a magnetic field move in

A

Clockwise

39
Q

What happens to the wire at 90 degrees in a motor

A

The loop of wire will stop rotating because the force will change direction

40
Q

How can we stop the forces from changing direction at 90 degrees

A

Use a Split ring commutator

41
Q

What does a split-ring commutator do

A

It switches the direction of the current when the loop passes 90 degrees

42
Q

What is the generator effect

A

a potential difference can be induced in a conducting wire when there is movement between the conductor and magnetic field

43
Q

What are the ways that an induced potential difference is created

A
  • When a coil of wire is moved in a magnetic field
  • A magnet is moved into a coil of wire
44
Q

When does the direction of the current switch

A

When the direction of movement switches

45
Q

When is the generator effect visible

A

When the wire passes through the magnetic field

46
Q

What are the factors affecting the size of the induced potential difference

A

Strength of the magnetic field
Speed of the wire
Number of turns of coil

47
Q

What occurs when a magnet is moved into a coil of wire

A

A current is induced in the wire which creates its own magnetic field which opposes the movement of the magnet

48
Q

What is an alternator

A

A coil of wire rotating in a magnetic field

49
Q

What is the coil connected to in an alternator

A

Two metal rings - commutators

50
Q

What is the role of commutators in an alternator

A

To allow the current to pass out of the coil when the wire passes through the magnetic field

51
Q

Each side of the wire connects onto …

A

An individual commutator

52
Q

When does the alternator experience the highest potential difference

A

When the coil is horizontal because the wire is sweeping through the magnetic field lines at the highest possible rate

53
Q

When is the potential difference of an alternator zero

A

When the coil is vertical because the coil is moving parallel to the field

54
Q

Why does an alternator produce an alternating current

A

Because the two sides of the coil are attached to two different rings

55
Q

How can the alternating-current be increased

A

Strengthening the magnetic field
Increasing the area or turns of coil
Increasing the rotation speed of the coil

56
Q

What current does a dynamo produce

A

Direct current

57
Q

What’s the difference between a dynamo and an alternator

A

A dynamo produces a direct current and contains a split ring commutator

58
Q

Why don’t the direction of the potential difference and current reverse when the coil rotates

A

As the original side of the commutator is connected to the original direction

59
Q

What does a moving coil loudspeaker contain

A

A coil of wire attached with thin sheet of plastic (diaphragm)

60
Q

What does the end of the coil of wire sit on top of

A

A permanent magnet

61
Q

What happens when sound waves hit the diaphragm 

A

They cause it to vibrate

62
Q

What happens when the diaphragm vibrates

A

The coil of wire moves in and out through the magnetic field and induces a potential difference

63
Q

Why does the potential difference which direction in a microphone

A

Because the coil moves backwards and forwards through the magnetic field

64
Q

What is the frequency of the soundwaves equal to 

A

The frequency of the changing potential difference

65
Q

How is a loudspeaker produced

A

The changing pattern of potential difference is passed through an amplifier and into a moving coil loudspeaker

66
Q

What does a transformer contain

A

Two wires wrapped around an inner core

67
Q

What’s the names of the two coils in transformers

A

Primary and secondary coil

68
Q

Why is iron used in transformers

A

It is easily magnetised
It increases the strength of the magnetic field 

69
Q

What is the primary coil connected to

A

An alternating current

70
Q

What happens when the current flows through the primary coil

A

It generates a changing magnetic field

71
Q

What happens once the magnetic field is transmitted along the iron core

A

It passes through the secondary coil

72
Q

What occurs when the changing magnetic field passes through the secondary coil

A

It induces a potential difference

73
Q

Why do transformers only work with an alternating current

A

Because a changing magnetic field is needed to induce a potential difference

74
Q

What type of transformer has less turns on the primary coil than the secondary coil

A

Step up transformer

75
Q
A



SEP Physics Weydon (13 decks)

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