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Physics > Magnets (paper2) > Flashcards

Magnets (paper2) Flashcards

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1
Q

What is the national grid

A

A system of wires and cables

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2
Q

What happens when electricity flows through a wire

A

It gets warm

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3
Q

Where is there significant energy loss in the national grid

A

In the transmission lines

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4
Q

If the voltage of electricity is increased what decreases

A

The current

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5
Q

When the current is smaller less what is transferred

A

Energy

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6
Q

What happens when less energy is transferred

A

Efficiency is improved

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7
Q

What kilo-voltage do power stations produce electricity at

A

25kV

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8
Q

What changes the 25kV to 400kV

A

Transformers

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9
Q

What is reduced before being sent into factories and buildings

A

The voltage

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10
Q

What does a step up transformer do

A

It increases the voltage and decreases the current at the same time

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11
Q

What does a step down transformer do

A

Decreases voltage and makes current higher

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12
Q

What is a transformer made up of

A

Two coils of insulted wire wound onto an iron core

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13
Q

Is there an electrical connection between the two coils of wire

A

No

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14
Q

Where is electricity supplied to in a transformer

A

The primary coil

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15
Q

How many turns are there in the primary coil

A

5 turns

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16
Q

How many turns in secondary coil

A

10 turns

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17
Q

What’s the voltage in the primary coil

A

10V

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18
Q

What’s the voltage in the secondary coil

A

20V

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19
Q

What type of current do transformers use

A

Alternating current

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20
Q

What does the alternating current in the primary coil create

A

A continuously changing magnetic field

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21
Q

What does the iron core carry

A

The magnetic field into the secondary coil

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22
Q

What does the changing magnetic field induce

A

A changing potential difference in the secondary coil

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23
Q

Where is the potential difference greater

A

In the secondary coil as it has more coils

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24
Q

What’s the potential difference in the transformer equation

A

PD across primary coil divided by PD across secondary coil is equal to the number of turns in the primary coil divided by number of turns in secondary coil

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25
Q

What’s the electrical power equation

A

Current x PD

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26
Q

How do you find the current in either coil

A

PD across primary coil x current in primary coil = PD across secondary coil x current in secondary coil

27
Q

What type of magnet is a bar magnet

A

Permanent because it’s always magnetic

28
Q

What does a piece of magnetic material become when in a magnetic field

A

An induced magnet

29
Q

How can we find the magnetic field

A

By using plotting compasses

30
Q

Name some pieces of equipment that contain magnets

A

Electric motors, generators and loud speakers

31
Q

Where is the field strongest on a plotted magnetic field

A

Where the lines are closest together

32
Q

The behaviour of compasses prove what

A

That the earth has a magnetic field

33
Q

What is earths magnetic field thought to be cause by

A

Electric currents in the molten outer core

34
Q

What is the outer core made up of

A

Iron and nickel

35
Q

What causes a magnetic field

A

A current flowing through a wire

36
Q

What does the direction of the magnetic field depend on

A

Direction of current

37
Q

The strength of the magnet field depends on what

A

The strength of the current

38
Q

What’s a solenoid

A

A wire made into a coil

39
Q

The field inside the coil does what

A

Join together to form a very strong field

40
Q

The fields outside the solenoid do what

A

Cancel each other out to form a weak field

41
Q

What is a coil with a current running though it called

A

An electromagnet

42
Q

How can the electromagnet be made stronger

A

By putting a piece of iron inside the coil

43
Q

What does the iron do inside the coil

A

Becomes a temporary magnet

44
Q

What’s the motor effect

A

Using a current to flow through two rails to produce a force

45
Q

The force is greatest when…

A

The wire is at right angles to the magnetic field

46
Q

What us magnetic flux density

A

Strength of magnetic field

47
Q

Show Flemings left hand rule

A

Thumb - force
Fore - field
Middle - current

48
Q

What is used to cause rotation in electric motors

A

Force on a conductor in a magnetic field

49
Q

What do carbon brushes do

A

Make electrical contacts between the circuit and motor

50
Q

Why is the metal ring commutator split

A

So that the current changes direction every half turn

51
Q

What does the split ring commutator ensure

A

That the force on the coil is always turning in the same direction

52
Q

What can a changing magnetic field do

A

Induce a voltage or potential difference in a wire and cause a current to flow

53
Q

The size of the induced potential difference depends on what

A

The number of turns in the coil and strength of the magnetic field

54
Q

A generator consists of what

A

A coil of wire that is rotated inside a magnetic field

55
Q

As the coil turns in a generator what is induced

A

A voltage

56
Q

What are the ends of the coil connected to

A

Slip rings

57
Q

What type of current does a generator produce

A

Alternating

58
Q

What do many electrical appliances need

A

Direct current

59
Q

What is a generator with a commutator called

A

A dynamo

60
Q

What do microphones convert

A

The pressure variations in the sound waves into current variations in electrical circuits

61
Q

What do the sound waves move

A

The diaphragm

62
Q

What do loudspeakers convert

A

Variation in electrical currents into sound waves

63
Q

What does the diaphragm produce

A

Sound waves

Physics (11 decks)

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