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edexcel igcse physics > EX unit two: electricity > Flashcards

EX unit two: electricity Flashcards

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1
Q

what colour is the earth wire

A

green and yellow

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2
Q

what colour is the live wire

A

red/brown

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3
Q

what colour is the neutral wire

A

blue

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4
Q

when wiring a three pin plug, what must the cable insulation be firmly gripped by

A

the cable anchor

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5
Q

all mains wiring is insulated with how many layers of insulation

A

2

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6
Q

why is all mains wiring insulated with 2 layers

A

it prevents the separate conductors (live, neutral and earth) from touvhing and prevents anyone touching a live (mains voltage) wire.

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7
Q

what does it mean when some appliances are double insulated (as well as the wiring)

A

that the outer casing is made out of an insulating material like plastic

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8
Q

why is it useful to double insulate appliances

A

so that no one gets an electric shock.

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9
Q

appliances with a metal outer casing that the user might touch must be…

A

earthed. the earth wire ensures that the outer casing is held at 0V and provides a very low resistance path for the current in the event of a fault in which the live wire touches the casing. this means the fault current will be very large and cause the fuse to blow immediatly, disconnecting the live supply.

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10
Q

what material are cartridge fuses

A

ceramic

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11
Q

what happens to a fuse once it has blown

A

it has to be replaced

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12
Q

what are circuit breakers

A

they perform the same job as fuses but are usually operated magnetically and may be reset by pressing a button.

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13
Q

what are RCCB’s

A

residual current circuit breakers

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14
Q

why do cables that carry electricity around our homes have very low electrical resistance

A

to make the unwanted conversion of electricity as small as possible.

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15
Q

power =

A

current x voltage

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16
Q

what is current measured in

A

amps (A)

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17
Q

what is voltage measured in

A

volts (V)

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18
Q

what is power

A

the rate at which electrical energy is converted in an appliance.

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19
Q

energy =

A

power x time

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20
Q

what is energy measured in

A

joules (J)

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21
Q

what does AC stand for

A

alternating current

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22
Q

what does DC stand for

A

direct current

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23
Q

what is alternating current

A

an alternating supply, like the mains, causes the current to change continuously, with electricity flowing in one direction then the other.

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24
Q

what is direct current

A

a direct supply, like batteries, makes electricity flow in one direction only.

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25
Q

why are metals good conductors of electricity

A

they have large numbers of de-localised electrons - electrons that aren’t bound to any particular atom in the structure of the metal. they are free to move, so when an electric force acts on the electrons it forces them to ‘drift’ in the direction of this electric force.

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26
Q

electric current is

A

the rate of flow of electric charge through ta conductor

27
Q

what is charge measured in

A

coulombs (C)

28
Q

current =

A

charge / time

29
Q

what is the symbol for charge

A

Q

30
Q

1 volt =

A

1 joule per couloumb

31
Q

energy =

A

charge x voltage

32
Q

what measures current

A

an ammeter

33
Q

what measures voltage

A

a voltmeter

34
Q

what does an ammeter tell you

A

how many coulombs of charge are passing through the lamp per second.

35
Q

what does voltage tell you

A

how many joules of energy are being converted to heat and light per coulomb of charge are passing through the lamp.

36
Q

is an ammeter placed in series or parallel

A

series

37
Q

is a voltmeter placed in series or parallel

A

parallel

38
Q

why is the current always the same as it flows through a series circuit

A

there are no alternative routes for the current to follow instead.

39
Q

why isn’t the current always the same as it flows through a parallel circuit

A

the current can split to take two or more routes.

40
Q

what appliances are wired in parallel

A

mains sockets outlets, mains lights and decorative lights.

41
Q

in a series circuit, the energy supplied by the cell is _________ between the components so the voltage across each component will _________

A

shared

vary

42
Q

in a parallel circuit, each component has its own connections to the cell so does not have to ________. the voltage across each branch in the circuit will be the ______.

A

share

same

43
Q

voltage =

A

current x resistance

44
Q

what is the symbol for resistance

A

R

45
Q

what is resistance measured in

A

ohms

46
Q

give a use for a resistor

A

simple lamp dimmer circuits or volume control in audio equipment

47
Q

resistors can be varied by

A

rotary or sliding action

48
Q

what are thermistors made from

A

semi-conductors

49
Q

thermistor’s resistance decreases as…

A

temperature increases

50
Q

what are LDR’s made from

A

semi-conductors

51
Q

more light shining on an LDR =

A

less resistance

52
Q

what are LDR’s used in

A

light sensing circuits

53
Q

diodes and LED’s only allow an electric current to pass in the direction of…

A

the arrow. one direction has huge resistance and the other has very little.

54
Q

insulators examples

A

rubber, glass, and many types of plastic

55
Q

protons are _____ charged

A

positively

56
Q

neutrons carry no ________ ________

A

electric charge

57
Q

electrons are ________ charged

A

negatively

58
Q

the charges on the proton and electron are?

A

equal in size but of opposite sign

59
Q

all atoms have equal numbers of electrons and protons, so the charges balance out and the atoms are overall,

A

neutral.

60
Q

unlike charges _______ and like charges ________

A

attract

repel

61
Q

what happens when you rub two materials together?

A

some electrons are torn from the surface of one of the materials and transferred to the other. the material which loses electrons now has a net positive charge because there are now more positively charged protons than electrons. the material that gained electrons now has more negatively charged electrons than positively charged protons and is therefore negatively charged

62
Q

uses of static electricity

A

inkjet printers, photocopiers, paint spraying, electrostatic precipitators.

63
Q

problems with static electricity

A

electric shocks, fuelling tanks and aircraft, handling microprocessors and computer ‘chips’.

edexcel igcse physics (13 decks)

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