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edexcel igcse physics > unit six: magnetism and electromagnetism > Flashcards

unit six: magnetism and electromagnetism Flashcards

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1
Q

magnets definition

A

a metal solid that is able to have magnetic charges through north and south poles

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2
Q

magnetic materials def

A

metal substance able to be attracted or repelled by a magnet

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3
Q

non - magnetic material

A

metal substance unable to be attracted or repelled by a magnet.

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4
Q

give some magnetic metals

A

iron, nickel, cobalt and steel

steel contains iron so is also magnetic

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5
Q

what is a magnetic field

A

the region around a magnet where a force acts on another magnet or on a magnetic field

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6
Q

what are the two poles on a magnet

A

north and south

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7
Q

what are hard magnetic materials used for

A

for things like magnets that we want to stay magnetised

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8
Q

what are soft magnetic materials used for

A

when we need something to magnetise and demagnetise easily

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9
Q

what are permenant magnets usually made of

A

steel or a range of modern magnetically ‘hard ‘materials

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10
Q

like poles…

A

repel

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11
Q

unlike poles…

A

attract

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12
Q

what is a magnetic field

A

the area where a magnetic material experiences force

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13
Q

what are magnetic field lines

A

they point from north to south (always)

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14
Q

how does the electric motor work

A

the current going through a loop of wire makes one side go up and one side go down so it spins. a split ring changes the direction of the current so that the rotation continues.

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15
Q

what machines make electricity

A

generators and alternators

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16
Q

how does a dynamo work

A

a little dynamo wheel presses up against the big bicycle wheel which makes it spin around. the dynamo wheel is attached to a magnet which spins. a solenoid is next to the magnet, and the moving magnetic field induces a current in the solenoid, which powers the lightbulb.

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17
Q

input voltage / output voltage =

transformer equation

A

number of turns on primary coil / number of turns on secondary coil

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18
Q

why are powerlines high voltage

A

if you have a large voltage, you can transfer the electrical energy with a small current. having a small current minimises heat loss.

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19
Q

electric power equation =

A 
power = voltage x current
P = V I
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20
Q

voltage =

V =

A

current x resistance

V = I x R

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21
Q

power =

P =

A

current squared x resistance

P = I^2 x R

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22
Q

which direction do magnetic field lines point

A

from north to south

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23
Q

if you place the north and south end of two permanent bar magnets near each other what do you create

A

a uniform magnetic field

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24
Q

what do compasses and iron align themselves with

A

magnetic fields

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25
Q

how can you set up an experiment to see magnetic field lines

A

put the magnets under a piece of paper, scatter with iron filings, and then tap until the iron filings form a clear pattern. or put the compass at the pole of a permanent magnet and follow the north arrow.

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26
Q

magnets affect…

A

magnetic materials and other magnets

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27
Q

both poles attracct…

A

magnetic materials

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28
Q

when magnetic materials are brought near to a magnet (into it’s magnetic field), that material acts as a…

A

magnet

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29
Q

what is it called when a magnetic material is brought near a permanent magnet and acts as a magnet

A

induced magnetism by the original magnet

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30
Q

does magnetism get stronger or weaker when you bring the magnets together

A

stronger

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31
Q

what does an electric current produce

A

a magnetic field

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32
Q

the larger the electric field, the stronger the…

A

magnetic field

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33
Q

what does the direction of the magnetic field depend on

A

the direction of the current

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34
Q

what is a solenoid

A

a coil of wire

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35
Q

describe the magnetic field inside a current-carrying solenoid

A

strong and uniform.

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36
Q

what is the magnetic field like outside a solenoid

A

like a bar magnet’s

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37
Q

so the ends of a solenoid act as the

A

north and south poles

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38
Q

what is the current-carrying solenoid called now as the ends act like a bar magnet

A

an electromagnet

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39
Q

soft magnetic material

A

if it loses it’s induced magnetism quickly

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40
Q

hard magnetic material

A

if it keeps it’s induced magnetism quickly

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41
Q

example of a soft magnetic material

A

iron

42
Q

example of a hard magnetic material

A

steel

43
Q

how do you increase the strength of an electromagnet

A

increase the number of coils, increase the current or add soft iron core through the middle,

44
Q

what does your thumb represent in the right-hand grip rule

A

direction of current

45
Q

what do your fingers represent in the right-hand grip rule

A

direction of the magnetic field

46
Q

when a charged particle moves through a magnetic field and it’s motion is not parallel, what does it experience

A

a force

47
Q

explain the motor effect

A

when a current is passed through a wire placed in a magnetic field, a force is produced which acts on the wire.

48
Q

what does a dot as a wire mean

A

the current is coming towards you or ‘out of the page’

49
Q

what does a cross as a a wire mean

A

the current is leaving the page, and going away from you.

50
Q

how do you make the force created using the motor effect stonger

A

increase the strength of the magnetic field or increase the current

51
Q

what does the thumb represent in fleming’s left hand rul

A

motion/force

52
Q

what does the index finger represent in fleming’s left hand rule

A

direction of magnetic field

53
Q

what does the middle finger represent in fleming’s left hand rule

A

current

54
Q

if you reverse the current or the magnetic field what happens

A

the direction of the force reverses.

55
Q

how does a loudspeaker work (1)

A

electric currents from a source, such as radio, pass through the coils of a speaker.

56
Q

how does a loudspeaker work (2)

A

these currents, which represent sounds, are always changing in size and direction, like vibrating sound waves.

57
Q

how does a loudpeaker work (3)

A

the field of the coil and the permanent magnet are therefore creating magnetic field patterns which are also changing in strength and direction.

58
Q

how does a loudspeaker work (4)

A

these fields in turn apply rapidly changing forces to the wires of the coil, which cause the speaker cone to vibrate..

59
Q

how does a loudspeaker work (5)

A

these vibrations create the soundwaves we hear.

60
Q

does a loudspeaker uses d.c. or a.c.

A

alternating current

61
Q

what does a loudspeaker consist of

A

electrical signals produced by an amplifier fed into a coil of wire in the speaker, which is wrapped around the base of a cone.

62
Q

what does a simple electric motor consist of

A

a single turn coil of wire that is free to rotate in a magnetic field about an axle. carbon brushes make contact with the ends of the coil that are connected to a commutator so that current can be passed through the coil.

63
Q

what speeds up an electric motor

A

more current
more turns on the coil
stronger magnetic field
a soft iron core in the coil

64
Q

explain why the electric motor’s coil rotates

A

when there is current in the loop of wire, one side of it will experience a force pushing it upwards, and the other will experience a force pushing it downwards, so the loop will begin to rotate.

65
Q

explain what happens as the loop in an electric motor reaches its vertical position

A

the momentum takes it past vertical. if the rotation is to continue, the forces on the wires must be reversed so that the wire at the top is pushed down and the wire at the bottom must be pushed up.

66
Q

how do we continue rotation of the loop in an electric motor

A

use a split ring to connect the loop of wire to the electrical supply. now each time the loop of wire passes the vertical position, the connections change, the direction of the current changes, and the forces on the different sides of the loop change direction.

67
Q

what is electromagnetic induction

A

when a conductor is in a changing magnetic field a voltage will be induced in the conductor

68
Q

how do you increase the size of the induced voltage

A

move the wire faster
use a stronger magnet so that there are more field lines ‘cut’
wrap the wire into a coil so that more pieces of wire move through the magnetic field

69
Q

explain electromagnetic induction

A

if a wire is moved across a magnetic field at right angles, a voltage is induced or generated in the wire. if the wire is part of a complete circuit there is current.

70
Q

how ELSE can you generate a voltage and current using induction

A

push a magnet into a coil. the cutting action between the field lines of the moving magnet and of the coil occurs.

71
Q

a voltage is induced when a conductor…

A

cuts through magnetic field lines

72
Q

a voltage is induced when magnetic field lines…

A

cut through a conductor

73
Q

the faster the lines are cut…

A

the larger the induced voltage.

74
Q

what type of current does a loudspeaker have to use

A

an alternating current

75
Q

describe a bicycle dynamo

A

as the cyclist pedals, the wheel rotates and makes a small magnet within the dynamo turn around. as this magnet turns, its magnetic field turns too. the field lines cut through the coil inducing a current in it. this current can be used to work the cyclists lights.

76
Q

how do larger a.c. generators work

A

generators rotate a coil in the magnetic field. as the coil spins, a current is induced tht changes direction every half turn. instead of a commutator, they have slip rings and brushes so that the contacts don’t swap every half turn. this means they produce a.c. voltage, which results in higher overall voltage and more peaks.

77
Q

what does a transformer consist of

A

a core made from thin sheets of a magnetically soft material clamped together. two separate coils of wire, insulated from one another, are tightly wound onto the core.

78
Q

how does a transformer work

A

it can be a step up or a step down. when an alternating voltage is applied across the primary coil (from an a.c. supply), the rapidly changing magnetic field will cause the magnetically soft core to magnetise and demagnetise quickly. this induces an a.c. current in the secondary coil.

79
Q

step up transformer:

A

increase the voltage
(decrease the current)
more coils on secondary coil than primary coil.

80
Q

step down transformer:

A

decrease the voltage
(increase the current)
they have more turns on the primary coil than on the secondary.

81
Q

input (primary) voltage / output secondary voltage =

A

number of turns on primary / number of turns on secondary

82
Q

Vp / Vs =

A

Np / Ns

83
Q

power =

A

voltage x current

84
Q

P =

A

V x I

85
Q

how efficent are transformers

A

100%

86
Q

input power =

A

output power

87
Q

Vp Ip =

A

Vs Is

88
Q

why does the national grid use transformers

A

to minimise energy losses through heat as current heats the wires

89
Q

P =

A

I squared x R

90
Q

describe the transmission of mains electricy by the national grid

A

power stations (25 kV) –> step up transformer –> power lines (132 kV) –> step down transformer –> homes and factories (0.23 kV)

91
Q

how do transformers increase voltage and decrease current

A

P = VI so the higher the voltage, the lower the current. (so the lower the voltage the higher the current).

92
Q

why are step down transformers used at the end of the national grid

A

to reduce the voltage so it’s safer and easier to use.

93
Q

why iron

A

it’s a soft magnetic material which is easily magnetised but does not retain it’s magnetism

94
Q

what is meant by magnetic field line

A

a line that shows the direction of the magnetic force/field

95
Q

how do you know from a data logger if the voltage is alternating/varying

A

it switches from being positive to negative

96
Q

describe the changes in a data logger when instead of one magnet being bounced through coil, it is two magnets

A

larger amplitude
lower frequency
alternate trace that diminishes

97
Q

how would curved magnets and a piece iron improve the performance of an electric motor

A

the force will be increased by a stronger field
radial magnetic field
coil remains in the field for a longer time

98
Q

when there is a current in the wire what is created around it

A

a magnetic field

99
Q

describe the magnetic field formed around a current carrying wire

A

quite weak and circular

100
Q

if the wire is made itnto a flat, single turn coil the magnetic field around the wire…

A

changes shape to go around the wire

101
Q

how do you increase the strength of a magnetic field around a current carrying wire

A

increasing the current in the wire

wrapping the wire into a coil or solenoid

edexcel igcse physics (13 decks)

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