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Electricity Flashcards

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1
Q

What are the two types of electrical supplies?

A

alternating current (ac) and direct current (dc)

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2
Q

What happens to the current in an ac supply?

A

it is constantly changing direction

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3
Q

How are alternating currents produced?

A

by alternating voltages in which the positive and negative ends keep alternating

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4
Q

What type of electricity supple is the the UK domestic mains supply (the electricity in your home) ?

A

ac supply

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5
Q

What voltage is the UK domestic mains supply?

A

around 230V

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6
Q

What is the frequency (how often the current changes direction) of the UK domestic mains supply?

A

50 Hz (hertz)
or 50 cycles per second

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7
Q

What type of current do cells and batteries supply?

A

direct current

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8
Q

What is a direct current?

A

a current that is always flowing in the same direction

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9
Q

How is a direct current created?

A

by a direct voltage in which the positive and negative ends of the source are fixed

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10
Q

How are most electrical appliances connected the the mains supply?

A

by three-core cables

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11
Q

What does a three-core cable mean?

A

they have three wires inside of them, each with a core of copper and a coloured plastic coating

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12
Q

What does the colour of the plastic insulation on each cable show?

A

its purpose, the colours are always the same for every appliance so this is easy to tell

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13
Q

What colour is the live wire?

A

brown

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14
Q

What colour is the neutral wire?

A

blue

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15
Q

What colour is the earth wire?

A

green and yellow

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16
Q

What is the purpose of the live wire?

A

provides the alternating potential difference from the mains supply

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17
Q

What is the purpose of the neutral wire?

A

to complete the circuit and carry away the current

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18
Q

What is the potential difference of the live wire?

A

about 230V

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19
Q

What is the potential difference of the neutral wire?

A

around 0V

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20
Q

What is the potential difference of the earth wire?

A

0V

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21
Q

What is the purpose of the earth wire?

A

for protecting the wiring and for safety as it stops the appliance casing becoming live, it doesn’t usually carry a current, it only does when there is a fault

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22
Q

What is the potential difference of your body (and the earth)?

A

0V

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23
Q

What would happen if you touch the live wire?

A

as your body and the earth are both at 0V a large potential difference is produced across your body and a current flows through you

this causes a large electric shock which could injure or even kill you

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24
Q

How is there still a danger of electric shock even even if a pulg socket or light switch is turned off?

A

although a current isn’t flowing there is still a potential difference in the live wire so if you made contact with it your body would provide a link between the supply and the earth so a current would flow through you

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25
Q

How can the connection between the live wire and the earth be particularly dangerous?

A

if the link provides a low resistance path to the earth a huge current (because of V=IR) will flow which could result in a fire

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26
Q

What is a material called if electrical charges can easily move through it?

A

a conductor

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27
Q

What is an example of a good conductor?

A

metals

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28
Q

What is a material called if electrical charges cannot easily move through?

A

an insulator

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29
Q

What are 2 examples of good insulators?

A

plastics and rubbers

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30
Q

What is a static charge?

A

an electric charge which cannot move

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31
Q

Where are static charges usually found?

A

on electrical insulators

32
Q

What charge can static charges have?

A

positive or negative

33
Q

How can a static charge build up on a conductor?

A

if it’s isolated (nowhere for the charge to flow to)

34
Q

When certain insulating materials are rubbed together what can happen?

A

friction causes negatively charged electrons to be transferred from one to the other

35
Q

How are electrostatic charges produced?

A

by the movement of electrons

36
Q

What happens when an electrical charge builds up on an object?

A

the potential difference between the object and the earth increases

37
Q

What can happen is the potential difference between an object and the earth gets large enough?

A

electrons can jump across the gap between the charged object and the earth (called a spark)

38
Q

What else can electrons jump between other than a charged object and the earth?

A

a charged object and any earthed conductor that is nearby

39
Q

When two elecrically charged objects are brought close together what do they exert on each other?

A

a non-contact force

40
Q

opposite charges _______

A

attract

41
Q

like charges ______

A

repel

42
Q

What is the attraction/repulsion between charges known as?

A

electrostatic attraction/repulsion

43
Q

What will electrostatic attraction/repulsion forces cause objects to do?

A

move if they can

44
Q

What happens to the electrostatic attraction/repulsion forces the further apart the objects are?

A

they get weaker

45
Q

What are 2 examples of electrotatic attraction/repulsion force?

A

two charged rods, one suspended by a piece of string so free to move

rubbing a ballon on your hair
electrons: hair to balloon

46
Q

What is an electric field created around?

A

any electrically charged object

47
Q

The closer you get to the object the __________ the electric field is.

A

stronger

48
Q

How can you show an electric field around an object?

A

by using field lines

49
Q

Where do electric field lines point from and to?

A

from positive charge towards negative charge

50
Q

Where are field lines drawn?

A

at right angles to a charged object’s surface

51
Q

The closer field lines are the __________ the field is.

A

stronger

52
Q

What does a charged object placed inside the electric field of another charged object experience?

A

a non-contact force

53
Q

What is a charged object placed inside the electric field of another charged object experiencing a non-contact force caused by?

A

the electric fields of each object interacting with each other

54
Q

What does a charged object placed inside the electric field of another charged object cause?

A

the attraction or repulsion between two objects

55
Q

What can a high potential difference cause?

A

a strong electric field between a charged object and an earthed object

56
Q

What can a strong electric field between a charged object and an earthed object caused by a high potential difference cause in terms of electrons?

A

electrons in the air particles are removed (ionisation)

57
Q

What is air normally?

A

an insulator

58
Q

What happens when the air is ionised?

A

it becomes much more conductive so a charge can flow through it (a spark)

59
Q

What does a voltmeter measure?

A

potential difference

60
Q

How are voltmeters connected?

A

across the component, in parallel

61
Q

What do ammeters measure?

A

current

62
Q

How are ammeters connected?

A

in line with a component, in series

63
Q

What is an electric current?

A

a flow of electric charge

64
Q

What are the positive and negative ends of cells?

A

positive terminal is the longer line
negative terminal is the shorter line

65
Q

Which direction does current flow around a circuit?

A

flows from positive to negative

66
Q

What is current measured in?

A

amperes, A

67
Q

What is the current equivalent to?

A

the rate of flow of charge

68
Q

What is the unit of charge?

A

coulombs (C)

69
Q

What does a circuit need in order for a charge to flow?

A

it needs to be a complete (closed) circuit and needs to have a source of potential difference

70
Q

What is potential difference?

A

the driving force that pushes the charge around

71
Q

What is the unit for potential difference?

A

volts, V

72
Q

What is resistance?

A

anything in the circuit which reduces the flow of current

73
Q

What is the unit for resistance?

A

ohms, Ω

74
Q

What determines the current flowing through a component?

A

the resistance and potential difference across the component

75
Q

What is an ohmic conductor?

A

a conductor that has a constant resistance for any current through it

Physics (7 decks)

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