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CC-2224 Physics Paper 2 Topics > P15(Electromagnetism) > Flashcards

P15(Electromagnetism) Flashcards

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1
Q

What is a magnetic field

A

The region around the magnet

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2
Q

Like poles …

A

Repel

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3
Q

Unlike poles …

A

Attract

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4
Q

Where is the magnet the strongest

A

At the poles because magnetic field lines are denser at the poles

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5
Q

Where is the magnet the weakest

A

In the middle because field lines are less dense

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6
Q

What are the 3 magnetic metals

A

Iron, nickel and cobalt

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7
Q

What is induced magnetism

A

When an unmagnetised magnetic material can be magnetised by placing it in a magnetic field

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8
Q

The Magnetic filed lines of a bar magnet curve around from the ….

A

North Pole of the bar magnet to the South Pole

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9
Q

For a freely suspended magnet its north seeking pole will point …

A

Towards geographical north

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10
Q

For a freely suspended magnet its south seeking pole will point …

A

Towards geographical south

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11
Q

How to do the right hand rule

A

-A current carrying conductor has a magnetic field around it
-Point a thumb towards the direction of the current
-Wrap fingers around the conductor
-this gives the direction of the magnetic field

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12
Q

What is a solenoid

A

A hollow coil of insulated wire

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13
Q

The magnetic field lines around a wire are …

A

Circles centred on the wire in a plane perpendicular to the wire

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14
Q

The magnetic field lines in a solenoid are …

A

Parallel to its axis and are all in the same direction

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15
Q

What is a uniform magnetic field

A

the magnetic field lines are parallel

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16
Q

How do you produce a magnetic field around a solenoid

A

When a current is passed through the wire

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17
Q

Increasing the current in a solenoid …

A

Increases the strength of the magnet

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18
Q

Reversing the direction of the current in a solenoid …

A

Reverses the magnetic field lines

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19
Q

What is an electromagnet

A

a solenoid in which the insulated wire is wrapped around an iron core

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20
Q

Where are electromagnets used

A

-scrapyards
-circuit breakers
-electric bells and relays

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21
Q

How does an electromagnet work in a circuit breaker or electric bell

A

Attracts an iron armature which opens a switch

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22
Q

An electric motor has a …

A

Coil that turns when a current is passed through it

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23
Q

What is the motor effect

A

When a force can act on a wire in a magnetic field when current is passed through the wire

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24
Q

How do you increase the size of the force in the motor effect

A

-increase the current
-use a stronger magnet
-increase the number of coils

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25
Q

What does the size of the force depends on

A

The angle between the wire and the magnetic field lines

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26
Q

The force (in motor effect) is ….

A

-Greatest when the wire is perpendicular to the magnetic field lines
-zero when the wire is parallel to the magnetic field lines

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27
Q

What does Flemings left hand rule show

A

The direction of the force on the wire

28
Q

How to do the left hand rule

A
29
Q

What does the size of the force on the conductor depend on

A

-the current in the conductor
-the length of the conductor
-the magnetic flux density of the magnetic field

30
Q

What is the formula that relates force, magnetic flux density,current,length

A
31
Q

What is magnetic flux density

A

A measure of the strength of a magnetic field

32
Q

How does the coil spin when a current is passed through the coil

A

-A force acts on each side of the coil due to the motor effect
-The force on one side is in the opposite direction to the force on the other side

33
Q

What are the parts of an electric motor

A

-concave shape magnets
-coil(armature)
-split ring commutator
-brushes

34
Q

What do the concave shape magnets do

A

keep rotating the coil perpendicular to the direction of the magnetic field to exert maximum force

35
Q

What is the coil(armature)

A

Rectangular coil of insulated wire which is forced to rotate

36
Q

What is the split ring commutator and what does it do

A

-made up of metal contacts attached with a coil and rotate with it
-their job is to reverse the direction of the current every half turn so that the coil rotates in the same direction

37
Q

What are brushes and what do they do

A

-made from graphite which is a conductor and slippery and low friction
-they make contact between the slip rings commutator and battery contacts

38
Q

Forces on either side of the coil ….

A

-equal in magnitude
-opposite direction
-forces do not share the line of action

39
Q

What is the generator effect

A

When there is a relative motion between the conductor and a magnet, alternating PD is produced

40
Q

A generator contains …

A

Coils of wire that spin a magnetic field

41
Q

What is electromagnetic induction

A

When a conductor crosses through the lines of a magnetic field a potential difference is induced

42
Q

The direction of an induced current always…

A

Opposes the original change that caused it

43
Q

How do you increase the induced PD in the generator effect

A

-stronger magnet
-move the magnet/conductor faster
-longer conductor

44
Q

How is a simple AC generator made

A

Made up of a coil that spins in a uniform magnetic field

45
Q

How do AC generators work

A

-As the coil rotates, Magnetic flux linking to the coil changes which induces alternating pd
-When the side of the coil moves parallel to the field lines, induced pd is zero
-As the coil rotates, magnetic flux linking to the coil increases and so does induced pd
-When sides of the coil cuts through the magnetic field lines at right angles, induced pd is maximum
-For a next 1/4 turn pd reduces to zero again
-For next 1/2 turn, induced pd reaches maximum and then to zero but in the negative direction

46
Q

How is a simple DC generator made

A

Has a split ring commutator instead of two slip rings

47
Q

How do DC generators work

A

-As the coil rotates, split ring commutator reconnects the coil in the opposite direction in the circuit every half turn
-This happens each time the coil is perpendicular to the magnetic field lines
-Induced PD does not change direction
-Induced PD varies from max to zero twice each cycle and does not change polarity

48
Q

What is a microphone

A

A microphone converts sound signals to electrical signals

49
Q

How does a microphone work

A

-An insulated voice coil placed in a magnetic field moves back and forth, when sound hits the diaphragm
-There is relative motion between a coil and a magnet
-This induces electrical signals in the voice coil

50
Q

How does a loudspeaker work

A

-Voice coil is placed between the poles of a permanent magnet
-Diaphragm is connected to the voice coil
-Electrical signals are passed on to the coil in the magnetic field
-Diaphragm feels a force back and forth due to AC
-Cone vibrations produce sound waves

51
Q

Transformers are used to …

A

Increase or decrease the size of an alternating potential difference

52
Q

A transformer only works with an …

A

AC because a changing magnetic field is necessary to induce AC in the secondary coil

53
Q

What are transformers made from

A

-a primary coil
-a secondary coil
-an iron core

54
Q

How does a transformer work

A

-Alternating current passing through the primary coil generates an alternating magnetic field in the iron core
-The lines of the alternating magnetic field in the iron core pass through the secondary coil
-The magnetic field in the secondary coil induces an alternating potential difference

55
Q

What do step up transformers do

A

Increase the size of an alternating potential difference

56
Q

What do step down transformers do

A

Decrease the size of an alternating potential difference

57
Q

What is the transformer equation

A
58
Q

For a step up transformer the number of secondary turns is …

A

-Greater than the number of primary turns
-So the potential difference across secondary coil is greater than the potential difference across primary coil

59
Q

For a step down transformer the number of secondary turns is …

A

-Less than the number of primary turns
-So potential difference across secondary coil is less than the potential difference across the primary coil

60
Q

Transformers are …

A

100% efficient

61
Q

What is the formula if 100% efficiency is assumed

A
62
Q

How is PD induced in the secondary coil in the transformers

A

-Alternating PD in the primary coil induces alternating magnetic field
-This alternating magnetic field links with the secondary coil
-This induces alternating PD in the secondary coil
-If there are more coils in secondary coil, induced PD is higher

63
Q
A
64
Q
A
65
Q
A
66
Q
A

CC-2224 Physics Paper 2 Topics (10 decks)

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