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Physics > P15 Magnetism and electromagnets > Flashcards

P15 Magnetism and electromagnets Flashcards

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1
Q

give three magnetic materials

A
  • iron
  • nickle
  • cobalt
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2
Q

what is meant by magnetic material

A

metals that are attracted by magnets and are attracted to either pole of a magnet

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3
Q

where is the magnetic force strongest on a pernament magnet

A

at the poles

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4
Q

what are the two poles

A
  • north
  • south
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5
Q

what are the two types of magnets

A
  • induced
  • pernament
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6
Q

what are induced magnets

A

materials made magnetic temporarily, always attracted to a magnet and then act as magnets to other materials

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7
Q

what direction do magnetic fields travel

A

from the north pole to the south pole

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8
Q

what do like poles/charges do

A

repel

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9
Q

what do opposite poles/charges do

A

attract

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10
Q

what happens when a current flows through a wire

A

it creates a magnetic field around the wire

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11
Q

what way does current always flow

A

from positive to negative

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12
Q

how can you determine a magnetic field

A

using compasses
compasses normally point north, by putting them around a wire we can tell if a field is either clockwise or anti-clockwise

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13
Q

what is the right hand grip rules used to find

A

the direction of the magnetic field

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14
Q

explain the right hand grip rule

A

with the thumb of the right pointing in the direction of the current, the way your fingers curl is the direction of the magnetic field

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15
Q

what does a dot to represent the wire is like in a diagram for electromagnetic field

A

that the current if flowing up wards

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16
Q

what does a cross to represent the wire is like in a diagram for electromagnetic field

A

that the current is flowing down

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17
Q

how can the magnetic fields strength be increased from a current

A

increase the current

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18
Q

what type of force is magnetism

A

non-contact

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19
Q

how can the force on a wire be increased

A

increase the current and the length of the wire

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20
Q

what is a solenoid

A

a coiled up peice of wire

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21
Q

what does coiling a wire into a solenoid do to the magnetic field through the wire

A

the magnetic field inside the solenoid is strong and uniform
and the magnetic field around the solenoid is similar in the shape of a bar magnet

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22
Q

what does adding an iron core inside a solenoid do and why

A

turns it into a electromagnet because the iron core becomes induced whenever a current flows through the wire

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23
Q

do induced magnets attract and repel

A

no only attract

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24
Q

what is an electromagnet

A

a magnet whose magnetic field can be turned on and off with an electric current

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25
Q

what are the three uses of electromagnets

A
  • circuit breakers
  • relay circuits
  • an electric bell / cranes
    (pick things up - act as a switch in another circuit)
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26
Q

how are electromagnets used in circuit breakers

A

as the current increases so does the magnetic field of the electromagnet. This attracts the metal switch and breaks the circuit

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27
Q

how are electromagnets used in electric bells

A
  • current enters the circuit causing the electomagnet to be magnetised
  • this atttracts the arms and causes the bell to be struck
  • the ‘make or break’ switch turns off
  • cycle repeats
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28
Q

how are electromagnets used in relay circuits

A
  • the current flows and the electromagnet attracts the iron arm
  • the arm pivots and pushes switches together completing the circuit
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29
Q

why are electromagnets useful in relay circuits

A

they switch on high voltage machineray that would risk shock if using a standard switch

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30
Q

what is the motor effect

A

when a current-carrying wire is in the presence of a magnetic field experiences a force and moves as the wire interacts with the magnetic field

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31
Q

why does the motor effect occur

A

because as they current carrying wire creates it’s own magnetic field it interacts with the permanet magnetic field and the resultant magnetic field causes a force

32
Q

what is used to measure the strength of a magnetic field

A

Magnetic flux density (Tesla (T))

33
Q

what is the equation that corresponds force, field strength, current and the wire length

A

force = field strength x current x length of wire
F = BIL

34
Q

what is F = BIL used to find

A

the magnitude of the motor effect

35
Q

what is used to find the direction of the motor effect

A

Flemmings left hand rule

36
Q

what is each finger in the Flemmings left hand rule

A
  • Thumb = force (motion)
  • finger 1 = field direction (n > s)
  • finger 2 = current direction ( + > -)
37
Q

what does a commutator do

A

change the direction of the current every half turn to allow a motor to continuously rotate by swapping the contacts to the DC supply

38
Q

what makes a motor spin faster

A
  • more turns on the coil
  • using a stronger magnet
  • using an iron core
  • using a bigger current
39
Q

what is the cummutator used in the motor effect

A

split ring commutator

40
Q

how can the direction of spin of a simple DC motor be reversed

A
  • changing direction of current
  • changing direction of magnetic field
41
Q

what is the other name for the generator effect

A

electromagnetic induction

42
Q

what is the generator effect

A

the induction of a potential difference (and a current if there’s a complete circuit) in a wire which is moving relative to a magnetic field, or experiencing a change in the magnetic field

43
Q

how can the size of potential difference induced from the generator effect be increased

A
  • move magnet/coil faster
  • use a stronger magnet
  • have more turns on the coil of wire
44
Q

how can the direction of the current in the generator effect be changed

A
  • moving the magnet/ coil in the opposite direction
  • swapping the direction of the magnet being used
45
Q

when do you use Faraday’s right hand rule

A

to find out the direction of induced current from motion in the generator effect

46
Q

what are each other the fingers used for in faraday’s right hand rule

A
  • thumb = force (motion)
  • finger 1 = magnetic field (n > s)
  • finger 2 = induced current ( + > - )
47
Q

how are microphones used with the generator effect

A
  • sound waves make diaphragm vibrate
  • = coil of wire vibrates around a magnet
  • this induces a potential difference
  • p.d has the same frequency as original sound wave
48
Q

what is the other name for an AC generator

A

an altinator

49
Q

when is potential difference greatest in an altinator

A

when parallel to field lines

50
Q

when is the potenital difference zero in an altinator

A

when perpendictular to field lines

51
Q

what is the other name for a DC generator

A

dynamo

52
Q

how can you make an AC generator DC

A

add a split ring commutator

53
Q

if we use an altinating current in a conductor what type of magnetic field will be produced

A

an altinating magnetic field

54
Q

if there is an altinating magnetic field what does this mean for size and direction

A

it is constantly changing

55
Q

if you double the number of coils in a transformer what will happen to the pd

A

it will double too

56
Q

what are transformers

A

something which reduces current and increases voltage, made up of an iron core and an insulated wire

57
Q

why are transformers needed to transport electricity

A

to maintain efficiency

58
Q

what is the equation relating voltage and number of turns on a transformer

A

(voltage on primary coil / voltage on secondary coil) = (number of turns on primary coil / number of turns on secondary coil)

59
Q

how does a transformer work

A
  • AC flows in the primary coil
  • this creates an alternating magnetic field in primary coil
  • the magnetic field from the primary coil cuts through the secondary coil
  • this induces a voltage and current in the secondary coil
  • the current in the seconary coil is also AC
60
Q

what is the difference between step up and step down transformers

A
  • step up has more turns on secondary coil
  • step down has more turns on primary coil
61
Q

how can you work out the input power of a transformer

A

primary current x primary potential difference

62
Q

what uses the motor effect

A
  • electrical motors
  • loudspeakers
63
Q

how do electric motors work

A
  • in a simple DC motor, force acts in opposite directiosn of a current carrying wire
  • this causes a rotation
  • a split ring commutator then swaps the contacts every half turn to keep the motor rotating the same direction
  • THE MOTOR EFFECT
64
Q

how does a loudspeaker work

A
  • an AC is sent through a coil attatched to the base of a paper cone
  • the coil surronds one pole of a permanent magnet and is surrounded by the other pole
  • this causes a force on the coil
  • so vibrations in the current make the cone vibrate which creates a sound wave
  • the frequency of the sound wave is the same as the frequency of the AC
65
Q

describe how an altinator works

A
  • alternators rotate a coil in a magnetic field
  • as the coil spins a current is induced in the coil ~ this current changed direction every half turn
  • slip rings ensure that the contacts don’t swap every half turn
  • an AC pd is produced
66
Q

what do oscilloscopes show for alernators and dynamos

A

how the potential different generated changes over time

67
Q

what generator is this pd time graph of

A

alternator

68
Q

what generator is this pd time graph of

A

dynamo

69
Q

how do microphones work

A
  • sound waves make the diaphragm vibrate
  • the diaphragm vibrating makes a coil of wire vibrate
  • the coil of wire vibrates around a magnet
  • this induces a pd
  • the induced pd has the same frequency as the original sound wave
  • GENERATOR EFFECT
70
Q

what are the two types of transformer

A
  • step-up
  • step-down
71
Q

what type of core is used in a transformer

A

iron

72
Q

if there are more coils what does this do to the voltage

A

increase it ~ more coils = more volts

73
Q

what is the equation for coils on the wire and voltage

A

(voltage on primary coil / voltage on secondary coil) = (number of coils on primary / number of coils on secondary)

74
Q

if the secondary coil has more turns than the primary what type of transformer is it

A

step up

75
Q

if the primary coil has more turns than the secondary what type of transformer is it

A

step down

76
Q

how can you work out the input power of a transformer

A

power = primary current x pirmary voltage

Physics (13 decks)

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