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Physics GCSE > Electromagnetism > Flashcards

Electromagnetism Flashcards

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1
Q

What is a permanent magnet?

A

A magnet that is always magnetised and produces its own magnetic field

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2
Q

What is an induced magnet?

A

A magnet that only has a magnetic field when induced by another magnet

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3
Q

Examples of magnetic materials

A

Iron, cobalt, steel, nickel

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4
Q

What is the force between like poles?

A

Repel

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5
Q

What is the force between unlike poles?

A

Attracts

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6
Q

What happens to field strength as distance decreases?

A

It increases

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7
Q

What type of magnet is the Earth?

A

A permanent magnet

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8
Q

How do we know the Earth is a permanent magnet?

A

A compass will always point to the North pole

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9
Q

How do you show magnetic field lines?

A

Iron filings or plotting compasses

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10
Q

What is the right hand thumb rule?

A

The direction of your fingers is the direction of the field and the direction of your thumb is the direction of the current

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11
Q

What is a solenoid?

A

A coil of current-carrying wire

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12
Q

How can the strength of a magnetic field of a solenoid be increased?

A

Increase current, more turns of wire, placing turns closer together, putting a soft iron core into the middle of a solenoid

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13
Q

What are uses of electromagnets?

A

Scrapyards, school gates, speakers, microphones, doorbells

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14
Q

What is the motor effect?

A

If a current carrying wire is placed in a magnetic field the wire will move

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15
Q

What does Flemings left hand rule show us?

A

Thumb - Motion/force
Fore finger - Magnetic field
Second finger - Current

All should be at a right angle to each other

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16
Q

What is the equation for force?

A

Force = magnetic flux density x current x length

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17
Q

How many amps is in a milliamp?

A

1000 amps

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18
Q

Which way does the magnetic field act?

A

From North to South

19
Q

What is a DC a motor?

A

A coil or wire in a magnetic field

20
Q

How does a DC motor work?

A
  1. When a current flows through the coil, a magnetic field is created
  2. This magnetic field interacts with the magnetic field from the motor and creates a force
  3. There’s an equal and opposite force on each side of the coil because the current on each side of the coil is flowing in opposite directions
  4. This force causes the motor to rotate
  5. When the coil has rotated 180 degrees, the current is now flowing in the opposite direction to before
  6. This means that the coil would experience a force in the opposite direction
  7. To prevent this a split ring commutator changes the direction of every half turn due to two halves of the coil swapping from one carbon brush to another
  8. This allows for the motor to experience a force in the same direction at any position within the field of the permanent magnet
  9. The commutator disconnects the current every half turn but momentum keeps the motor rotating
21
Q

How does an AC motor work?

A
  1. When a current flows through the coil, a magnetic field is created
  2. This magnetic field interacts with the magnetic field from the motor and creates a force
  3. There’s an equal and opposite force on each side of the coil because the current on each side of the coil is flowing in opposite directions
  4. This force causes the motor to rotate
  5. When the coil has rotated 180 degrees, the current is now flowing in the opposite direction to before
  6. This means that the coil would experience a force in the opposite direction
22
Q

What is the difference between an AC and DC motor?

A

An AC motor doesn’t need a commutator because the current is alternating but a DC motor does

23
Q

What can you do to make the motor spin in the direction?

A

Reverse direction of current or reverse direction of magnetic field

24
Q

What can you do to make the motor faster?

A

Increase the current, increase the magnetic flux density, increase the number of turns in the coil

25
Q

How can you induce potential difference?

A

Moving a coil of wire into a magnetic field or moving a magnet into a coil of wire

26
Q

What is the generator effect?

A

The motion of a wire in a magnetic field induces current

27
Q

What happens when a magnet is stationary?

A

No current is induced

28
Q

How can you increase the induced current using the generator effect?

A

Faster movement, stronger magnetic field, more turns in the coil, larger area of coils

29
Q

What is a dynamo?

A

A DC generator

30
Q

How does a Dynamo work?

A

The coil is spun making it experience a changing magnetic field which induces potential difference. If the coil is in a complete circuit then a current is induced

31
Q

What is the commutator used in a dynamo called?

A

Slip ring commutator

32
Q

What happens when a magnet moves in the opposite direction?

A

Current is increased in the opposite direction

33
Q

Why do dynamos use slip ring commutators?

A

To make DC from AC

34
Q

What is an alternator?

A

An AC generator

35
Q

What happens if the dynamo is rotated twice?

A

The frequency would double

36
Q

How potential difference induced from dynamos?

A

When the coil moves in a directions where it’s cutting through the magnetic field lines, PD is the greatest
As the coil continues to rotate PD decreases
When the coil moves in the same directions as the magnetic field lines no PD is induced
As the coil continues to rotate PD increases
Until it reaches a maximum when it moves through horizontal, cutting through magnetic field lines again

37
Q

How does an alternator work?

A

A rectangular coil is made to spin in a uniform magnetic field, causing an alternating current to be induced in the coil

38
Q

How does an electric motor work?

A

The force in a current carrying wire in a magnetic field pushes one side of the coil down and the other side up

39
Q

What does a changing magnetic field around a conductor produce?

A

A potential difference that can create a current

40
Q

What does a loudspeaker consist of?

A

A coil that vibrates when AC flows through it

41
Q

How does a loudspeaker work?

A
  1. The current creates a magnetic field
  2. This magnetic field interacts with the permanent magnet in the loudspeaker, causing a force
  3. As the current changes direction, this then vibrates a cone
  4. The vibrating cone causes pressure variations in the air and forms longitudinal sound waves
42
Q

How does a microphone work?

A
  1. The sound waves cause a flexible diaphragm to vibrate
  2. The vibration causes a coil to move around a permanent magnet
  3. This changing magnetic field around the coil induced a potential difference
  4. Because the coil is in a complete circuit, this then induces a current
  5. This current in the electrical output from the microphone
43
Q

What do loudspeakers do?

A

Turns electrical signals into sound waves

44
Q

What do microphones do?

A

Turn sound waves into electrical signals

Physics GCSE (9 decks)

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