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Electricity Flashcards

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
How can the connection between the live wire and the earth be particularly dangerous?
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
26
What is a material called if electrical charges can easily move through it?
a conductor
27
What is an example of a good conductor?
metals
28
What is a material called if electrical charges cannot easily move through?
an insulator
29
What are 2 examples of good insulators?
plastics and rubbers
30
What is a static charge?
an electric charge which cannot move
31
Where are static charges usually found?
on electrical insulators
32
What charge can static charges have?
positive or negative
33
How can a static charge build up on a conductor?
if it's isolated (nowhere for the charge to flow to)
34
When certain insulating materials are rubbed together what can happen?
friction causes negatively charged electrons to be transferred from one to the other
35
How are electrostatic charges produced?
by the movement of electrons
36
What happens when an electrical charge builds up on an object?
the potential difference between the object and the earth increases
37
What can happen is the potential difference between an object and the earth gets large enough?
electrons can jump across the gap between the charged object and the earth (called a spark)
38
What else can electrons jump between other than a charged object and the earth?
a charged object and any earthed conductor that is nearby
39
When two elecrically charged objects are brought close together what do they exert on each other?
a non-contact force
40
opposite charges _______
attract
41
like charges ______
repel
42
What is the attraction/repulsion between charges known as?
electrostatic attraction/repulsion
43
What will electrostatic attraction/repulsion forces cause objects to do?
move if they can
44
What happens to the electrostatic attraction/repulsion forces the further apart the objects are?
they get weaker
45
What are 2 examples of electrotatic attraction/repulsion force?
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
What is an electric field created around?
any electrically charged object
47
The closer you get to the object the __________ the electric field is.
stronger
48
How can you show an electric field around an object?
by using field lines
49
Where do electric field lines point from and to?
from positive charge towards negative charge
50
Where are field lines drawn?
at right angles to a charged object's surface
51
The closer field lines are the __________ the field is.
stronger
52
What does a charged object placed inside the electric field of another charged object experience?
a non-contact force
53
What is a charged object placed inside the electric field of another charged object experiencing a non-contact force caused by?
the electric fields of each object interacting with each other
54
What does a charged object placed inside the electric field of another charged object cause?
the attraction or repulsion between two objects
55
What can a high potential difference cause?
a strong electric field between a charged object and an earthed object
56
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?
electrons in the air particles are removed (ionisation)
57
What is air normally?
an insulator
58
What happens when the air is ionised?
it becomes much more conductive so a charge can flow through it (a spark)
59
What does a voltmeter measure?
potential difference
60
How are voltmeters connected?
across the component, in parallel
61
What do ammeters measure?
current
62
How are ammeters connected?
in line with a component, in series
63
What is an electric current?
a flow of electric charge
64
What are the positive and negative ends of cells?
positive terminal is the longer line negative terminal is the shorter line
65
Which direction does current flow around a circuit?
flows from positive to negative
66
What is current measured in?
amperes, A
67
What is the current equivalent to?
the rate of flow of charge
68
What is the unit of charge?
coulombs (C)
69
What does a circuit need in order for a charge to flow?
it needs to be a complete (closed) circuit and needs to have a source of potential difference
70
What is potential difference?
the driving force that pushes the charge around
71
What is the unit for potential difference?
volts, V
72
What is resistance?
anything in the circuit which reduces the flow of current
73
What is the unit for resistance?
ohms, Ω
74
What determines the current flowing through a component?
the resistance and potential difference across the component
75
What is an ohmic conductor?
a conductor that has a constant resistance for any current through it

Physics (7 decks)

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