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AQA Physics GCSE > Magnetism and Electromagnetism > Flashcards

Magnetism and Electromagnetism Flashcards

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1
Q

What are the two poles of a magnet?

A

North and south.

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2
Q

What do all magnets produce?

A

A magnetic field

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3
Q

What type of force is magnetism?

A

A non-contact force.

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4
Q

How can you show a magnetic field?

A

By drawing magnetic field lines.

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5
Q

What direction do the lines go towards in a magnetic field?

A

North to south.

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6
Q

If the magnetic field lines are closer together, what does this show?

A

The stronger the magnetic field.

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7
Q

Where is the magnetic field strongest?

A

At the poles.

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8
Q

What will happen if two opposite poles are put near each other?

A

They will attract.

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9
Q

What will happen if two of the same poles are put near each other?

A

They will repel.

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10
Q

Describe the method for using compasses to show the direction of magnetic fields.

A
  1. Place the compass at the north pole of a bar magnet. Mark on a dot where the compass is pointing.
  2. Move the compass so that the base of it is in-front of the marked dot.
  3. Record another dot where the compass is pointing.
  4. Repeat the last two steps, moving the compass around the bar magnet.
  5. Once the compass reaches the south pole, join up the dots to create lines.
  6. Repeat on the other side of the magnet.
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11
Q

How do compasses show the direction of magnetic fields?

A

Inside it, there is a tiny bar magnet. The compass needle points in the direction of the magnetic field it is in. When not near a magnet, the needle always points north as earth generates its own magnetic field. The core of the earth is magnetic.

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12
Q

What are the two types of thing a magnet can be?

A

Permanent or induced.

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13
Q

What are permanent magnets?

A

Magnets that produce their own magnetic field.

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14
Q

What are induced magnets?

A

Magnetic materials that turn into a magnet when put into a magnetic field.

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15
Q

What is the force between permanent and induced magnets?

A

attractive

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16
Q

What are magnetic materials?

A

Materials that are attracted to a magnet. Iron, Nickel, Cobalt and steel.

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17
Q

Complete the sentence: A ___________ ___________ creates a magnetic field.

A

moving charge

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18
Q

What happens when current flows through a wire?

A

A magnetic field is created around the wire.

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19
Q

What is the magnetic field of current flowing through a wire made up of?

A

concentric circles, perpendicular to the wire with the wire in the centre.

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20
Q

What is the right hand rule?

A

Hold hand in thumbs up.
Thumb represents the direction of current. Fingers represents the direction of the magnetic field.

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21
Q

What does the strength of the magnetic field produced by current flowing through a wire depend on?

A

The current and distance from the wire.

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22
Q

Complete the sentence: The _________ the current through a wire, or the ___________ to the wire you are, the ___________ the field is.

A

larger, closer, stronger

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23
Q

What is a solenoid?

A

A coil of wire.

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24
Q

How can you increase the strength of a magnetic field a wire produces?

A
  • wrap it into a coil called a solenoid
  • the more coils, the stronger the field
  • place a block of iron in the centre of the coil
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25
Q

What is the magnetic field inside a solenoid like?

A

strong and uniform - it has the same strength and direction at every point in that region.

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26
Q

What is the magnetic field outside of the solenoid like?

A

Like a bar magnet, lines point north to south.

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27
Q

What is an electromagnet?

A

A solenoid with an iron core. It can be turned on and off with an electric current.

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28
Q

What are electromagnets used for?

A
  • cranes, to pick up things made from magnetic materials in scrap yards
  • within circuits to act as switches
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29
Q

What are the uses of electromagnets?

A

Cranes - to attract and pick up things made from magnetic materials, e.g. scrap yards
Circuits - to act as switches
Electric bells
Car ignition circuits
Security doors

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30
Q

What is the motor effect?

A

When a current-carrying wire is put into a magnetic fields, they interact and can exert a force on the wire, causing it to move.

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31
Q

Complete the sentence: To experience the full force, the wire has to be ___ ° to the magnetic field.

A

90°

32
Q

What will happen in the motor effect if the wire runs parallel to the magnetic field?

A

It wont experience any force at all.

33
Q

Explain how a horseshoe magnet can be used to show the direction of force in the motor effect.

A

Apply a current to a set of rails inside the horseshoe magnet. A bar is placed on the rails, which completes the circuit. This generates a force that rolls the bar along the rails.

34
Q

How can the force of the motor effect be increased?

A

Stronger magnetic field
Higher current passing through the conductor

35
Q

How can you calculate the size of the force in the motor effect?

A

Force = Magnetic flux density (T) X current (A) X length (m)

36
Q

How can you find out the direction of the force acting on a conductor in a magnetic field?

A

Fleming’s left-hand rule.

  • using your left hand, point your First finger in the direction of the Field, point your seCond finger in the direction of Current and thuMb in the direction of Motion/force.
37
Q

What will happen to the direction of the force is either the current or magnetic field is reversed?

A

It will also be reversed.

38
Q

What is an electric motor?

A

A current-carrying coil of wire rotating in a magnetic field.

39
Q

What happens in a basic DC motor?

A

Forces act on the two side arms of a coil of wire that is carrying a current. Because the coil is on an axle and the forces act one up and one down, it rotates. The split-ring commutator swaps the contacts every half turn to keep the motor rotating in the same direction.

40
Q

How can the direction of the motor be reversed?

A

Reversing the current or field.

41
Q

What is the generator effect?

A

The induction of a potential difference (and current if there’s a complete circuit) in a wire which is experiencing a change in magnetic field.

42
Q

What does the generator effect induce?

A

a potential difference in a conductor.

43
Q

How does the generator effect work?

A

By moving a magnet in a coil of wire or moving a conductor in a magnetic field.

44
Q

What will happen if you move the magnet or conductor in the opposite direction?

A

The potential difference/ current will be reversed. And if the polarity of the magnet is reversed too.

45
Q

What happens if you move the magnet backwards and forwards?

A

The potential difference keeps swapping direction, which produces an alternating current.

46
Q

What causes the generator effect?

A

Rotation

47
Q

Complete the sentence: Induced current _________ the change that made it.

A

opposes

48
Q

What can change in magnetic field do to a wire?

A

Induce a current

49
Q

Complete the sentence: The magnetic field created my an induced current always acts ___________ ____ _________ that made it.

A

against the change

50
Q

How can you change the size of the induced potential difference?

A
  1. Increase the speed of movement - cutting more magnetic field lines in a given time.
  2. Increase the strength of the magnetic field (so more field lines that can be cut)
51
Q

Complete the sentence: Generators make use of the generator effect to ___________ ____ ___________.

A

Induce a current

52
Q

What do Alternators generate?

A

alternating current

53
Q

What do Dynamos generate?

A

direct current

54
Q

Explain how the generator effect works using alternators?

A
  1. Generators rotate a coil in a magnetic field (like a motor).
  2. As the coil (or magnet) spins, a current is induced in the coil. The current changes direction every half turn.
  3. Instead of split-ring commutator, alternators have slip rings and brushes so the contacts dont swap every half turn.
  4. This means they produce an alternating potential difference.
55
Q

How are dynamos different to alternators?

A

They work the same way but have a slip-ring commutator instead of slip rings. This swaps the connection every half turn to keep the current flowing in the same direction.

56
Q

What equipment can you use to see the generated potential difference?

A

An oscilloscope.

57
Q

What would the oscilloscope show for alternators?

A

A line that goes up and down, crossing the horizontal axis.

58
Q

What would the oscilloscope show for a dynamo?

A

A line that goes up and down (can be straight too) but always stays positive, doesn’t cross the horizontal axis.

59
Q

What is the height of the line at a given point on an oscilloscope?

A

The generated potential difference at that time.

60
Q

How does increasing the frequency of revolutions affect the overall potential difference?

A

It increases the overall pd and also creates more peaks too.

61
Q

How do loudspeakers work?

A

The motor effect.

  1. An AC is sent through a coil of wire attached to the base of a paper cone.
  2. The coil surrounds one pole of a permanent magnet and is surrounded by the other pole, so the current causes a force on the wire so cone moves.
  3. When the current reverses, the force acts in the opposite direction, causing the cone to move in the opposite direction too.
  4. So variations in the current make the cone vibrate, which makes the air around the cone vibrate creating variations in pressure that cause a sound wave.
  5. The frequency of the sound wave is the same as the frequency of the AC, so by controlling the frequency of ac you can alter the sound wave produced.
62
Q

What do microphones generate from sound waves?

A

current

63
Q

What are microphones?

A

Loudspeakers in reverse.
1. Sound waves hit a flexible diaphragm that is attached to a coil of wire, wrapped around a magnet.
2. This causes the coil of wire to move in the magnetic field, which generates current.
3. The movement of the coil (and so the generated current) depends on the properties of the sound wave - louder sounds make the diaphragm move further.
4. Microphones convert the pressure variations of sound waves into variations in current in an electric circuit.

64
Q

What effect do transformers use? To do what?

A

The generator effect to change the size of the potential difference.

65
Q

What only type of current do transformers work with?

A

alternating current

66
Q

How do transformers work?

A
  1. They have two coils of wire, the primary and the secondary, joined with an iron core.
  2. When an alternating PD is applied across the primary coil, the iron core magnetises and demagnetises quickly. This changing magnetic field induces an alternating PD in the secondary coil.
  3. If the second coil is part of a complete circuit, this causes current to be induced.
  4. The ratio between the primary and secondary potential differences is the same as the ratio between the number of turns on the primary and secondary coils.
67
Q

What is the ratio between the primary PD and secondary PD the same as?

A

The ratio between the number of turns in the primary and secondary coils.

68
Q

What is a step-up transformer?

A

It increases the potential difference. It will have more turns on the secondary coil than the primary coil.

69
Q

What is a step-down transformer?

A

It decreases the potential difference. They will have more turns on the primary coil than secondary coil.

70
Q

Give the equation linking input PD, output PD, turns on primary coil and turns on secondary coil.

A

Vp/Vs = np/ns

71
Q

Complete the sentence: Transformers are _____________ 100% efficient.

A

almost

72
Q

What can you assume with transformers when using the equations?

A

That the input power is equal to the output power since transformers are almost 100% efficient.

73
Q

Give the equation linking PD across secondary coil, current through secondary coil, PD across primary coil and current through primary coil.

A

Vs X Is = Vp X Ip

Secondary coil power output = Primary coil power output

74
Q

What is Fleming’s left hand rule used for?

A

To show the current, magnetic field and force in a motor.

75
Q

What are the two types of generators?

A

Alternators and Dynamos.

76
Q

What type of generator uses slip rings and brushes?

A

Alternator.

77
Q

Why do transformers have a core of iron?

A

To increase the strength of the magnetic field.

AQA Physics GCSE (8 decks)

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