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physics > Magnetism And Electromagnetism > Flashcards

Magnetism And Electromagnetism Flashcards

1
Q

Which direction does a compass point towards

A

The south pole

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2
Q

What is a magnet

A

An object that creates a magnetic field around it

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3
Q

In which direction do field lines travel in

A

From the north to the south pole

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4
Q

What is the difference between a magnetically hard material and a magnetically soft material

A

A magnetically hard material(or permanent magnet) retains its magnetism after being magnetized, whereas magnetically soft materials lose their magnetism easily and so are temporary magnets

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5
Q

Give examples of magnetic materials

A

Iron, cobalt, nickel, steel

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6
Q

Why is using a compass useful for drawing a magnetic field

A

Because the needle is a bar magnet which points towards the South Pole

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7
Q

What are three things that magnetic field lines show

A

The shape of a magnetic field
The direction of the magnetic force
The strength of the magnetic field

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8
Q

Give four examples of magnetic materials

A

Iron, nickel, cobalt, steel

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9
Q

Give an example of a magnetically soft material

A

Iron

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10
Q

Explain how you could induce magnetism on an iron nail

A

Place a permanent magnet near the nail
The permanent magnets magnetic field will induce magnetism on the iron nail
When the permanent magnet is moved away the nail will lose its magnetism

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11
Q

How can you use two permanent magnets to produce a uniform magnetic field pattern

A

Place the opposite sides of the poles next to each other

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12
Q

Why is the shape of the magnetic field of a solenoid similar to?

A

Similar to that of a bar magnet

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13
Q

Why does adding iron to a solenoid increase the magnetism

A

Because it is a soft magnetic material which can induce magnetism

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14
Q

How can you reverse the direction of the magnetic field?

A

You can reverse the direction of the current flow

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15
Q

What causes the hammer to hit the gong in an electric bell

A

When the iron in the coil is magnetized,
it attracts the iron armature towards it
And so it pulls the hammer

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16
Q

What stops the current from flowing in an electric bell

A

Once the iron armature hits the gong a gal is created in the circuit so current can no longer flow, so the magnet is no longer magnetized

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17
Q

The iron solenoid and magnetic field of the iron core

A
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18
Q

What is a uniform magnetic field

A

A magnetic field in which the strength and direction is all the same

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19
Q

How could you improve the experiment about using compasses to draw field lines of a magnet

A

1)make sure to look at the compass from above to avoid inaccurate angle
2)use a sharp pencil

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20
Q

In terms of the motor effect, at which angle is the force exerted in the wire going to be greatest

A

At 90 degrees

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21
Q

Why does a current carrying wire exert a force in a magnetic field

A

Because the wire itself when a current is passing through it creates a magnetic field around it.
So the overlapping of the two fields creates a force

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22
Q

Explain how an electric motor creates motion from an electric current

A

1)Current is turned on and because the direction of current flow is at 90 degrees to the magnetic field, the magnetic field of the coil and the magnetic field of the magnets interact and a force is exerted upwards (for example)
2)the other side of the coil also experienced a downwards force due to the overlapping magnetic fields
3) this causes the coil to rotate clockwise
4)when the coil is now vertical, the split ring commutator reverses the direction of the current, so that it continues to rotate
5)the split ring commutator continues to reverse the current after every half turn

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23
Q

What are four ways that you can increase the speed of a motor

A

-increase the current
-increases the number of turns around the coil
-make sure the current is 90 to the magnetic field
-use stringer magnets for a stronger magnetic field

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24
Q

Explain why when the magnetic field of the current is parralel to the magnetic field of thr magnets, no force is exerted

A

Because there is no interaction between the two magnetic fields, therefore no force is created

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25
Q

Explain how a loudspeaker works

A

1)an alternating current is passed through the coil of wire, which means that the current changes direction
2)the alternating current creates a changing magnetic field which creates a force as this magnetic field interacts with the magnetic field of the permanent magnet
3)because the direction of the current reverses, the direction of the force also changes, therefore the cone vibrates back and forth
4)this vibrates with air particles to create sound waves

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26
Q

Why is the size of the force and magnetic field changing in a loud speaker

A

Because of the alternating current

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27
Q

What creates a force in a loud speaker

A

The interaction of the magnetic field of the current and the magnetic field of the permanent magnet

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28
Q

What is it about the dc electric motor that keeps the loop continuously spinning

A

The loops own momentum
And the split ring commutators which reverse the direction of the current

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29
Q

At which interval does the split ring commutator change the direction of the current

A

After every half turn

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30
Q

What is a difference between the generator effect and the motor effect

A

In the motor effect, the wire already has a current going through it,
whereas in the generator effect a potential difference or current is induced in it

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31
Q

What is the generator effect

A

When a potential difference is induced due to the magnetic field of a conductor changing

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32
Q

Give two ways that a potential difference can be induced

A

When a conductor/coil cuts through a magnetic field
When a magnetic field cuts through a coil

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33
Q

When would you expect to see a potential difference created and when would you see a current created in terms of the generator effect

A

Potential difference when it’s a single wire or coil
Current when it’s a complete circuit

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34
Q

Explain how a potential difference is induced when a magnetic field moves relative to an electrical conductor

A

The magnetic field lines of the magnet cuts through
the turns on the coils
Inducing a potential difference in the coil

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35
Q

Explain how a potential difference is induced when an electrical conductor moves relative to a magnetic field

A

The electrical conductor cuts through the magnetic field lines
So a potential difference is induced in the wire

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36
Q

Explain how increasing the number of turns on a coil, increases the induced potential difference when a coil moves through a magnetic field

A

Because there is thus more pieces of wire to cut through the magnetic field lines

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37
Q

Explain how increasing the strength of the magnet increases the induced potential difference when a wire moves through a magnetic field

A

Because there are more magnetic field lines for the wire to cut through

38
Q

What are four ways that you can increase the induced potential difference

A

1)increase the speed that the wire/coil or magnet is moved
2)increase the number of turns of the wire
3)increase the size of the coil
3)increase the strength of the magnet

39
Q

Explain why increasing the size of the coil increases the induced potential difference

A

Because there is more surface area to cut through the magnetic field lines

40
Q

Explain why increasing the speed at which the coil is moved through the magnetic field lines increases the potential difference induced

A

Because magnetic field lines will be cut at a faster rate

41
Q

Explain how a bike Dynamo works

A

When the person pedals and makes the wheel rotate, a magnet rotates around
The magnetic field lines cut through the coil
Thus inducing a potential difference
And because the magnetic field is constantly changing direction, an alternating current is induced

42
Q

Why does a bike Dynamo produce an alternating current

A

Because the magnetic field is constantly changing direction, thus producing an alternating current

43
Q

Explain why a dc motor uses a split ring commutator

A

To switch the terminals to allow the current to flow in one direction, to produce a direct current

44
Q

Give two differences between a motor and an alternator

A

Motor converts electrical to mechanical energy
Alternator converts mechanical to electrical energy
Motor uses the motor effect which relies on the interaction of two magnetic fields
Alternator relies on the generator effect which relies on electromagnetic induction

45
Q

Explain what the potential difference is when the coil is parralel to the magnetic field lines

A

Potential difference is 0 because the coil is not cutting through any field lines

46
Q

Explain what the potential difference is when the coil changes direction

A

Potential difference is negative because the coil is still cutting through the magnetic field lines, but In the opposite direction

47
Q

Give three ways to increase the strength of the alternating current in an ac generator

A

1)increase the size of the magnetic field
2)increase the speed at which it moves through the magnetic field
3)Increase the number of turns on the coil
4)increase the area of the coil

48
Q

What are two things that increasing the speed that the coil rotates in an ac generator can do

A

Increases the potential difference
Increases the frequency of the alternating current

49
Q

How is electricity generated in a power station

A

Through an AC alternator

50
Q

How are high voltages transported throughout the city

A

On high levels supported by pylons

51
Q

Why is a step down transformer used at the end

A

Because it reduces the voltage and so is safer to use

52
Q

How is electricty transferred from a power station to the national grid and why

A

Through a step up transformer
Because it increases the voltage and reduces the current so that less energy is lost

53
Q

How many volts of electricity are transferred from the power station to the national gord

A

400 000volts

54
Q

How many volts of electricity is transferred from the national grid to homes

A

230 volts

55
Q

What is the equation to work out output voltage

A

Number of turns of primary /number of turns of secondary

Input primary voltage/output primary voltage

56
Q

What is the equation for power

A

Power = current x voltage

57
Q

What is another way to rewrite the equation for input voltage and output voltage

A

VpIp=VsIs

58
Q

What is the only type of current that transformers work with

A

An alternating current

59
Q

Explain how a transformer works

A

An alternating voltage is supplied to the primary coil,
Therefore a changing magnet field is created
Thus the secondary coil also induces this voltage

60
Q

How does electromagnetic induction work in a transformer

A

the secondary coil is able to induce a voltage
because an alternating potential difference is applied to the primary coil
which thus creates a changing magnetic field
And a changing magnetic field allows electromagnetic induction to occur

61
Q

Explain why a magnetically hard material would not be able to lift metal on a crane

A

Because magnetically hard materials do not lose their magnetism quickly
So it would retain its magnetism even after the current is turned off
And so would still be holding onto the iron and steel

62
Q

When a current is passed through an electromagnet, an iron bar is attracted to it. When the current turns off, the iron bar is no longer attracted. Explain how this happens

A

When a current is passed through, the electromagnet(or the solenoid) creates a magnetic field around it
This magnetic field induces magnetism in the iron bar which is then attracted to the electromagnet
When the current stops, there is no longer a magnetic field around the electromagnet so it loses its magnetism
And so the iron bar is no longer attracted to it

63
Q

What is a magnetically soft material

A

A material that loses its induced magnetism quickly

64
Q

What is a hard magnetic material

A

Material that retains its magnetism for longer

65
Q

Describe the magnetic field of a solenoid

A

Inside the solenoid there is a uniform magnetic field
And outside the solenoid, there is the magnetic field of a bar magnet

66
Q

Why will the motor stay stationary at 90 degrees from its starting position

A

Because the current will be parrallel to the magnetic field
as the force on the op arm will act upwards and the force on the bottom arm will act downwards

67
Q

What toe things can change the direction of the force

A

Reversing the direction of the current or the magnetic field

68
Q

What is electromagnetic induction

A

The creation of a voltage in a conductor due to a change in the magnetic field

69
Q

How can you make an ammeter move in the opposite direction when a magnet is moved through a coil

A

Move the magnet the other way through a coil
Change the pole sides

70
Q

Describe an experiment to show the magnetic field lines of a bar magnet

A

Place a compass near the magnet and draw a line where it is pointing
Move the compass and then draw another line towards where it’s pointing
Continue this for other points around the magnet
Join all the points together to show the field lines

71
Q

Suggest how you can reduce the magnetic field between two magnets

A

Make them more far apart from eachotehr

72
Q

Explain why a curved magnet is better for a motor

A

Because it means that the coil stays in the magnetic field for longer
(Because there is more time that the coil is perpendicular to the magnetic field)

73
Q

What does adding an iron core to the coil in a motor do

A

The iron core becomes magnetized
So increases the magnetic field, thus increasing the force

74
Q

A magnet is released from a great height into a coil.
Explain why and what the voltmeter readings show

A

A large voltage is induced
Because there are many magnetic field lines that have been cut

75
Q

Describe how you can discover magnetic field lines of a bar magnet (3)

A

Place the magnet under a piece of paper
Sprinkle iron fillings over it
Tap the paper gently to reveal the pattern

76
Q

Explain how you could produce a uniform magnetic field

A

Place two permanent bar magnets next to each other
With the North Pole of one magnet facing the South Pole of the other magnet
And make sure the magnets are close together but not too far apart
And so a uniform magnetic field will be created in the space between the two opposite poles

77
Q

The electrons in a metallic conductor is the flow of:

A negatively charged electrons
B negatively charged protons
C positively charged electrons
D positively charged protons

A

A

78
Q

Explain why on a voltmeter you may see a current that is moving up and down in an experiment where you put a magnet on a spring and drop it through a coil

A

Because a voltage is being induced when the magnetic field lines are cut,
When the magnetic moves slower, magnetic field lines are cut at a slower rate, so voltage induced is less

79
Q

Give two ways why a voltage can be alternating when you induce it by moving a magnet in and out of a coil

A

1)because the direction that the magnet moves in can vary
2)because the speed at which the magnetic field lines are being cut can vary

80
Q

If I increase the magnetic strength but decrease the time taken for a magnet to move through a coil, explain the changes that would occur on an alternating voltage graph

A

The amplitude would be higher because increased magnetic strength
But the frequency would be lower because it happens at a slower rate

81
Q

How is electromagnetic induction used in alternators to induce an alternating current

A

A coil spins through an electromagnetic field
This induces a potential difference, which due to the slip ring commutators causes the current to change direction, thus induces an alternating current

82
Q

How does a Dynamo generate current

A

A coil spins through a magnetic field
Which induces a current
And due to the split ring commutators, the current direction remains in one direction (because the coil keeps spinning in one direction)

83
Q

What happens to an electrical conductor when there is a change to the magnetic field

A

The Voltage is also changed

84
Q

What happens to an electrical conductor when it moves through a magnetic field

A

It induces a voltage

85
Q

What would happen if the current entering a transformer was DC instead of AC

A

The magnetic field would be constant, so nothing would be induced in the secondary coil

86
Q

Give one example of an induced magnet

A

Doorbell

87
Q

Give an example of a permanent magnet

A

Compass pointer

88
Q

Explain how you can use a compass to draw a magnetic field around a bar magnet

A

1)place a compass next to the bar magnet, and mark the direction it points in with a dot
2)place the compass in the new position it points in and mark the direction again with a dot
3)repeat for many different positions around the bar magnet
4)link all the dots with a smooth curve to show the magnetic field lines

89
Q

Describe the construction of an electromagnet

A

A current carrying wire
Is wrapped around in a coil
Around an iron core

90
Q

Two coils are placed together, but when the current in one of the coils is reversed (so is different to the direction of the other coil) they move away. Explain why

A

There is an interaction of magnetic fields
So a force is created of repulsion
And this specific force is because the magnetic field has reversed
Therefore the like poles are togther which repel eachither

91
Q

In between two bar magnets with a uniform magnetic field, explain how you would show that the strength of the magnetic field has increased

A

Draw the lines closer together

physics (10 decks)

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