Physics - magnetism and electromagnetism Flashcards

1
Q

Magnetic field

A

A region where other magnets or magnetic materials experience a force

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2
Q

What are the 4 magnetic materials

A

Iron
Cobalt
Steel
Nickel

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3
Q

In a magnetic field drawing in what direction do the lines go in

A

From north to south

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4
Q

In a magnetic drawing the closer together the lines are …

A

The stromger the magnetic field

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5
Q

The force between a magnet and a magnetic material is __________

A

Always attractive no matter the pole

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6
Q

How do compasses work

A

In a compass there is a tiny bar magnet. The north pole of this magnet is attracted to the south pole of any other magnet it is near, so the compass points in the direction of the magnetic field it is in.

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7
Q

When their not near a magnet where do compasses always point

A

North as the Earth generates its own magnetic field, which shows the inside (core) of the Earth must be magnetic.

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8
Q

What are the two types of magnets

A

Permanent and induced

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9
Q

Permanent magnets

A

Produce their own magnetic field

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10
Q

Induced magnets

A

Magnetic materials that turn into a magnet when they’re put into a magnetic field

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11
Q

The force between permanent and induced magnets is __________

A

always attractive

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12
Q

What happens when a current flows through a wire

A

A magnetic field is created around the wire

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13
Q

What is the magnetic field made up of

A

Made up of concentric circles perpendicular to the wire, with the wire in the centre

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14
Q

If you change the direction of the current how does this affect the direction of the magnetic field

A

Changes direction of the magnetic field

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15
Q

What is solenoid

A

Coil of wire with a permanent magnet inside of it

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16
Q

How can you increase the strength of the magnetic field using a solenoid

A
  • More turns in the coil
  • Increase strength of magnet
  • Increase current
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17
Q

Describe the magnetic field inside the solenoid

A

Strong and uniform - has the same strength and direction at every point in that region

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18
Q

Whats the point of putting an iron block in the centre of the coil

A

Increases the field strength of the solenoid as this iron core becomes an induced magnet whenever current is flowing.

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19
Q

What is a solenoid with an iron core called

A

An electromagnet

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20
Q

Why electromagnets useful

A

Because they’re so quick to turn on and off or because they can create a varying force

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21
Q

Uses of electromagnets

A
  • used in cranes to attract and pick up things
  • used with other circuits to act as switches
22
Q

When can cause the motor effect

A

When you put a current-carrying wire in a magnetic field

23
Q

How does the motor effect work

A

When a current-carrying wire is put between magnetic poles the magnetic field around the wire interacts with the magnetic field it has been placed in. This causes the magnet and conductor to exert a force on each other causing the wire to move.

24
Q

To experience full force where does the wire have to be

A

Exactly 90 degrees to the magnetic field

25
Q

The magnitude (strength) of a force increases with

A

The strength of the magnetic field
Amount of current passing throughout the conductor

26
Q

What are the three things that a force acting on a conductor in a magnetic field depends on

A
  • The magnetic flux density (strength of the magnetic field)
  • The size of the current
  • The length of the conductor thats in the magnetic field
27
Q

What happens in a basic DC motor

A

Forces act on the two sides arms of a coil of wire that’s carrying a current.

28
Q

Why does one force act up and one force act down (rotate) in electric motors and loudspeakers

A

Because the coil is on a spindle

29
Q

What does the split ring communicator do

A

Swaps the contacts every half turn to keep the motor turning in the same direction

30
Q

How can the direction of the motor be reversed

A
  • By swapping the polarity of the dc supply
  • swapping the magnetic poles over
31
Q

How do electric motors and loudspeakers

A

A cone with a coil of wire wrapped around one end is connected to an alternating current electric supply. The permanent magnet goes inside the coil of wire. As the. current passes through the coil it generates a magnetic field. The magnetic field from the coil now interacts with the magnetic field from the magnet which produces a resultant force causing the cone to move. This causes the cone to move in and out generating sound waves.

32
Q

How do we change the frequency that a cone vibrates in a speaker

A

By changing the frequency of the ac supply

33
Q

What happens if we increase the size of the current

A

We increase the amplitude of the vibration thus the volume.

34
Q

What happens if we move a wire up through a magnetic field

A

A voltage is induced across the end on the wire

35
Q

Induced potential

A

When a pd reverses

36
Q

Generator effect

A

The induction of a potential differences in a wire which is moving relative o a magnetic field or experiencing a change in magnetic field

37
Q

When do we get an induced current or induced potential

A

When we you move a wire through a magnetic field or if we keep the wire still and move the magnetic field.

Or

Putting a magnet through a coil of wire

38
Q

When do we only see the generator effect

A

When the wire passes through a magnetic field

39
Q

The induced potential difference is larger when

A

We use a stronger magnetic field
If we move the wire more rapidly
If we shape the wire into a coil (the more turns in a coil the better)

40
Q

Why is it hard for the magnet in a coil to push in and out

A

The induced current creates its own magnetic field which opposes the movement of a magnet. Eg. when we insert the north pole into the coil that end of the current also becomes a north pole repelling the magnet and making it harder to push in. When we pull the magnet out, that end of the coil becomes the south pole which attracts the magnet making it hard to pull out.

41
Q

Because the induced current makes it harder to move the magnet ….

A

We are doing work. We are transferring energy from the movement of the magnet into the movement of the current.

42
Q

An alternator

A

A device that makes use of the generator effect to generate alternating currents

43
Q

What do commutators do

A

Allow the current to pass out of the coil

44
Q

When is a pd induced in alternators

A

When a wire passes through the magnetic field

45
Q

Hows does an alternator produce an alternating pd

A

Because the two sides of the coil are attached to two different rings an alternator produces an alternating pd and current.

46
Q

How do we increase the size of the ac

A

Increase the strength of the magnetic field
Increase the number of turns on coil or area
Increase rotation speed of coil

47
Q

Dynamo current

A

Produces a direct current. PD and current do not reverse when the current rotates

48
Q

Split ring commutator

A

Has two sides separated by a gap each side of coil is connected to one side of the commutator

49
Q

What does the split ring commutator ensure the coil rotates in one direction

A

The split-ring commutator swaps the positive and negative connections every half turn.
Therefore, the direction of the current through the coil reverses every half turn.
This means that the forces acting on the coil will always be acting in the same direction.
This causes the coil to rotate continuously in one direction.

50
Q
A