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PHYSICS > MAGNETISM AND ELECTROMAGNETISM > Flashcards

MAGNETISM AND ELECTROMAGNETISM Flashcards

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1
Q

What is a magnetic field?

A

A region where other magnets or magnetic materials experience a force

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2
Q

What direction do magnetic field lines go in?

A

They go from north to south (come out of north pole and into south pole)

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3
Q

What does it mean if magnetic field lines are closer together?

A

The force is stronger

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4
Q

What happens when two poles of a magnet are put near each other?

A

They will exert a force on each other either attractive or repulsive

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5
Q

What happens when a magnet and magnetic material are put near each other?

A

There is an attractive force between the two

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6
Q

Why does a compass point in the direction of the magnetic field it is in?

A

Because the north pole of the magnet is attracted to the south pole of any magnet it is in

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7
Q

Why does a compass always point north if it isn’t near a magnet?

A

Because Earth generates its own magnetic field which shows the inside core of the Earth is magnetic

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8
Q

What are permanent magnets?

A

They produce their own magnetic field

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9
Q

What are induced magnets?

A

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

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10
Q

What is the force between permanent and induced magnets always going to be?

A

Attractive

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11
Q

What happens when you take away the magnetic field from an induced magnet?

A

It quickly loses its magnetism and stops producing a magnetic field

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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 rule shows you the direction the magnetic field is going around a wire (which has a current)?

A

The right hand thumb rule

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14
Q

What creates a stronger magnetic field around a wire (with a current)?

A

Larger current
Closer to the wire you are

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15
Q

What is a solenoid?

A

A coil

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16
Q

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

A

By wrapping the wire into a coil called a solenoid

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17
Q

Why does a solenoid produce a stronger magnetic field?

A

Because the field lines around each loop of wire line up with each other
Therefore lots of field lines point in the same direction lose to each other

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18
Q

What is the magnetic field like inside a solenoid?

A

Strong and uniform (same strength and direction at every point)

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19
Q

What is the magnetic field like outside a solenoid?

A

Same as one round a bar magnet

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20
Q

How can you increase the field strength of solenoid even more (not adding more coils)?

A

A put a block of iron in the centre of the coil

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21
Q

What happens to the iron core in the middle of a solenoid?

A

It becomes an induced magnet

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22
Q

What happens when you stop the current going through a solenoid?

A

The magnetic field disappears

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23
Q

What is an electromagnet?

A

A solenoid with an iron core
The magnetic field can be turned on and off with an electric current

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24
Q

What can electromagnets be used for?

A

Cranes to attract and pick up things
Within circuits to act as switches

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25
Q

What is the motor effect?

A

When a conductor (wire) is put between magnetic poles
The magnetic field around the wire interacts with the magnetic field it has been placed in
The magnet and wire exert a force on each other
The wire moves

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26
Q

When will a wire experience the full force of a magnetic field?

A

When it is it at 90 degrees to the magnetic field (not parallel)

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27
Q

What happens to the magnitude of a force as the magnetic field strengthens?

A

The magnitude of the force increases

28
Q

What increases the current passing through a conductor?

A

The force increasing

29
Q

What does the force acting on a conductor in a magnetic field depend on?

A

Magnetic flux density (how many field lines there are in a region)
Size of current
Length of conductor

30
Q

What is fleming’s left hand rule?

A

Motion (thumb)
Field
Current

31
Q

How does a basic dc motor work?

A

Forces act on two side arms of a coil of wire thats carrying a current
Coil is on a spindle so the forces act one up and on down so it rotates

32
Q

What is a split ring commutator?

A

Swaps the contacts every half term in a basic dc motor to keep the motor rotating in the same direction

33
Q

Which direction does current always flow?

A

From positive to negative

34
Q

Which direction does a magnetic field always flow?

A

From north to south

35
Q

How do loudspeakers work?

A

AC current sent through coil of wire attached to base of paper cone
Coil surrounds one pole (S) of permanent magnet and is surrounded by the other pole (N)
Current causes force to act on coil which causes cone to move
When current reverses cone moves in opposite direction
Variation in current causes cone to vibrate and creates variations in pressure which cause a sound wave

36
Q

How can you alter the frequency of a sound wave?

A

By altering the frequency of the AC

37
Q

What is the generator effect?

A

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

38
Q

What does the generator effect do?

A

It creates a potential difference in a conductor
Also creates a current if he conductor is part of a complete circuit

39
Q

How do you create a generator effect?

A

By moving a magnet in a coil of wire
OR
Moving a conductor in a magnetic field

40
Q

What usually is a conductor?

A

Wire (made into a solenoid sometimes)

41
Q

What can the generator effect also be known as?

A

An electromagnetic induction

42
Q

What happens when you shift the magnet side to side (generator effect)?

A

Creates a little ‘blip’ of the current if the conductor is part of a complete circuit

43
Q

What happens when you move the magnet in the opposite direction (generator effect)?

A

Potential difference/current will be reversed (same if polarity of magnet is reversed)

44
Q

What happens if you keep the magnet moving backwards and forwards (generator effect)?

A

You produce a potential difference that keeps swapping direction (an alternating current)

45
Q

How do generators produce an alternating current?

A

Turn magnet which changes the magnetic field through the coil
This induces a pd and a current flows through wire
Half turn means direction of magnetic field reverses and so does pd and current
Turning magnet in same direction will keep reversing pd and current each half turn

46
Q

What happens when you change the magnetic field around a wire?

A

A current is induced

47
Q

What happens when you change the magnetic field around a wire and a current is induced?

A

The magnetic field created by an induced current acts against the change that made it

48
Q

How can you increase the size of the potential difference by changing the magnetic field (generator effect)?

A

Increase speed of movement of magnetic field
Increase the strength of the magnetic field

49
Q

How do alternators work?

A

Rotate a coil in a magnetic field
Coil spins so current is induced which changes direction every half turn
Produce alternating potential difference

50
Q

What do slip rings and brushes do in alternators?

A

Instead of slip ring commutator so the contacts don’t swap every half turn

51
Q

What current do alternators generate?

A

Alternating current

52
Q

What current do dynamos generate?

A

Direct current

53
Q

How do dynamos work?

A

Same as alternators but have a split ring commutator which swaps the connection every half turn to keep the current flowing in the same direction

54
Q

What do oscilloscopes show?

A

How the potential difference generate in the coil changes over time

55
Q

What do oscilloscopes look like for alternating currents?

A

Goes up and down crossing the horizontal axis (positive and negative)

56
Q

What do oscilloscopes look like for direct currents?

A

Goes up and down but stays above the horizontal axis (stays positive)

57
Q

What are mircophones?

A

Loudspeakers but in reverse

58
Q

How do microphones work?

A

Sound waves hit flexible diaphragm attached to coil of wire wrapped around magnet
Coil of wire moves in magnetic field which generates current
Convert pressure variations of a sound wave into a current in circuit

59
Q

What does the movement of coil depend on in a microphone?

A

The properties of the sound wave
e.g. louder sound wave makes the diaphragm move further

60
Q

What do transformers do?

A

They change the size of the potential difference of an alternating current

61
Q

What do transformers consist of?

A

Two coils of wire (primary and secondary) joined with an iron core

62
Q

How do transformers work?

A

AC applied across primary coil
Iron core magnetises and demagnetises quickly
Changing magnetic field induces alternating potential difference in secondary coil
Causes current to be induced in secondary coil (if circuit)

63
Q

What is the ratio between the primary and secondary potential differences the same as?

A

The ratio between the number of turns on the primary and secondary coils

64
Q

What do step up transformers do?

A

Increase the potential difference
They have more turns on the secondary coil than primary coil

65
Q

What do step down transformers do?

A

They decrease the potential difference
They have more turns on their primary coil than secondary coil

PHYSICS (12 decks)

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