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Yr 10-11 Physics > Unit 4 > Flashcards

Unit 4 Flashcards

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1
Q

what do opposite poles do

A

attract

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2
Q

what to do similar poles do

A

repel

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3
Q

what direction do magnetic field lines always point

A

north to south

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4
Q

in attraction, how do the field lines point

A

they point north to south and flow between the 2 points

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5
Q

in repulsion, what is the nature of the field lines

A

they point in opposite directions and bend away from each other

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6
Q

how is the strength of the magnetic field seen

A

the density of the field lines

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7
Q

what happens when permanent magnets attract a magnetic materia

A

a magnetic field is induced in the material

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8
Q

what does hard magnetic materials mean

A

they are hard to magnetise and also hard to demagnetise

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9
Q

what does soft magnetic materials mean

A

they are easy to magnetise and demagnetise

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10
Q

what is an electromagnet

A

when a coil of wire carries current and a magnetic field is induced

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11
Q

what are properties of permanent magnets

A

constant magnetic field
cannot be switched on and off
north and south poles cannot be switched
made with hard magnetic materials

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12
Q

what are properties of electromagnets

A

variable strength magnet field
can be switched on and off quickly
north and south poles can be changed by changed the direction of current flow
made from soft magnetic materials

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13
Q

what are the charge carriers in electrical devices

A

electrons

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14
Q

why are conductors able to conduct

A

there electrons are free to move around

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15
Q

why are insulators unable to conduct

A

there are no free electrons to move

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16
Q

what is a charge

A

an electric charge that can be positive or negative

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17
Q

what do unlike charges and like charges do

A

unlike charges attract
like charges repel

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18
Q

what happens if there is an equal number of positive and negative charges

A

it is neutral

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19
Q

what happens when an object loses electrons

A

it becomes positively charged

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20
Q

what happens when an object gains electrons

A

it becomes negatively charged

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21
Q

what is the symbol for electrical charge and how is it measured

A

symbol is Q
measured in coulombs(C)

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22
Q

what is static electricity

A

occurs when friction between 2 insulators causes electrons to be transferred from one surface to another

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23
Q

what are electrical fields

A

when 2 charged particles approach each other, they experience a force
the space in which the electric charge experiences a force is called the electric field

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24
Q

what is current

A

the measure of the flow of charge
also known as rate of flow of charge

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25
Q

how can current be increased

A

current flow can be increased by:
making each charged particle move faster
increase the number of charged particles
increased the amount of charge each particle carries

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26
Q

formula for current

A

I = Q/T
current = charge/time

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27
Q

what is used to measure current

A

an ammeter

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28
Q

what is conventional current

A

electrons are repelled from the negative terminal of the battery and attracted to the positive terminal
conventional current is the opposite(positive to negative)

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29
Q

what are alternating currents(AC)

A

when the electrons continously change direction

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30
Q

what are direct currents(DC)

A

electrons flow in one direction

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31
Q

what is electromotive force

A

the phenomena that enables charge to flow around the whole circuit
determined by the battery voltage

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32
Q

what is electromotive force measured in

A

volts

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33
Q

what is potential difference

A

the energy needed per charge to flow between two points in a circuit
work done per unit charge

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34
Q

what is potential difference measured with

A

measured with a voltmeter and always placed parallel across a component

35
Q

formula for potential difference and electromotive force

A

V = W/Q
v = voltage
w = energy
q = charge

36
Q

what is resistance

A

the measure of how much opposition there is to the flow of current
measured in ohms

37
Q

what is the formula for resistance

A

R = V/I
r = resistance
v = potential difference
i = current

38
Q

how is the length of the wire related to resistance

A

resistance is directly proportional to the length of the wire

39
Q

how is the thickness of the wire related to resistance

A

it is inversely proportionate
thicker the wire, smaller the resistance

40
Q

what is ohms law

A

electric current is directly proportionate to voltage and inversely proportionate to resistance

41
Q

how can electrical power be calculated

A

P = IV
p = power
i = current
v = potential difference

42
Q

what is a diode

A

only allows current to flow in one direction
requires a small amount of power to activate
non ohmic device

43
Q

what is a light emitting diode(LED)

A

regular diode that lights up when current flows through

44
Q

what is a series circuit

A

the current flows in one loop and voltage is shared throughout. if there are multiple lamps, they will all be dimmer

45
Q

what is a parallel circuit

A

there is more than one loop of current
voltage is the same for all loops

46
Q

advantages of parallel circuits

A

the potential difference across each lamp will be equal to the e.m.f. means every lamp will be brighter
each loop can be turned off separately

47
Q

featurs of series circuits

A

the current will be the same at all points
the potential difference across all resistors is shared
sum of the pd = battery power

48
Q

how to find total resistance in series circuits

A

by adding resistance of all the components up

49
Q

features of parallel circuits

A

the current flowing into a junction is equal to the sum of currents flowing out of a junction
each resistor experiences the same p.d as the power supply

50
Q

how to find total resistance in parallel circuits

A

1/total resistance = 1/resistance of component 1 + 1/resistance of component 2

51
Q

what is Faradays law

A

a wire close to a changing magnetic field will experience an induced electromotive force

52
Q

how can EMF be induced

A

moving a magnet so that its field lines are cut by the wire
moving a wire across a magnetic field

53
Q

what is flemings right hand rule

A

thumb is direction of motion of the wire
first finger is direction of magnetic field
second finger is direction of the current

54
Q

what is Lenz’s law

A

the direction of the induced emf opposes the charge that creates it

55
Q

how can the strength of the induced emf be increased

A

increasing the force or speed at which the wire or hte magnet is moved
increasing the strength of the magnet

56
Q

what happens when the wire moves parallel to the magnetic field

A

an emf is not induced

57
Q

how can the induced emf be decreased

A

decreasing the number of turns in the wire

58
Q

how do AC generators work

A

a rectangular coil of wire continously rotates within a magnetic field and generates an induced emf
the slip rings allow the direction of the induced emf to alternate and cause an ac currect

59
Q

what is the purpose of carbon brushes in AC generator

A

make an electrical connection between the rotating coil and circuit

60
Q

what will the voltage output look like in an AC generator

A

the voltage output will have peaks and troughs as the magnet turns from being parallel to perpendicular

61
Q

what magnetic field does a direct current create

A

it creates a constant magnetic field

62
Q

what magnetic field does an alternating current create

A

an alternating magnetic field

63
Q

what is the magnetic field around a current carrying wire

A

circular

64
Q

whats a solenoid

A

when wires are arranged in a coil, the resulting magnet is the same is that of a bar magnet

65
Q

how can the magnetic field of a solenoid be made stronger

A

increase the current through the solenoid
increase the number of turn in the wire

66
Q

what happens when the solenoid is supplied with an alternating current

A

changes the direction of the magnetic field every half cycle

67
Q

what happens when a current carrying wire is placed within a magnetic field

A

the wire experiences a force and can move

68
Q

how can the size of the force be increases when a current carrying wire is placed in a magnetic field

A

increase the current in the wire
increase the number of individual wires
increase the strength of magnetic field
increase the length of the wire

69
Q

what is the right hand rule used for

A

used to find emf induction

70
Q

what is left hand rule used for

A

used for DC motors

71
Q

what is the difference between AC and DC motors

A

DC motors have a cell that supply it power
AC motors get their current through an induced emf

72
Q

how can DC motors spin quicker

A

increase the strength of the magnetic field
increase the number of turns of wire in the coil
increase the current to the coil from the power supply

73
Q

what are transformers

A

device that can increase or decrease the size of an alternating electromotive force

74
Q

what do step up transformers do

A

increase the voltage

75
Q

what do step down transformers do

A

decrease the voltage

76
Q

what do transformers consist of

A

a primary coil- alternating current supplied through her
soft iron core-allows transition of magnetic flux to a secondary coil
a secondary coil-the output of the transformer and will have more or less coils

77
Q

formula for transformers

A

Vp/Vs = Np/Ns
Vp-voltage applied to primary coil
Np-number of turns in the coil
Vs-voltage applied to secondary coil
Ns- number of turns

78
Q

how many turns does the secondary coil have in a step up

A

the secondary coil has more turns than the primary coil

79
Q

how many turns does the secondary coil have in a step down transformer

A

has fewer turns than the primary coil

80
Q

what current do transformers require

A

they require alternating currents

81
Q

what is formula for 100% efficiency in a transformer

A

IpVp = IsVs

82
Q

how can the efficiency of a transformer increase

A

using low resistance coils to reduce power wasted
using a laminated core which consists of layers of iron separated by layers of insulation

83
Q

how can power loss in a wire be calculated

A

P=1^2R

Yr 10-11 Physics (7 decks)

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