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Physics 9-1 iGCSE Oxford AQA > Electricity > Flashcards

Electricity Flashcards

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1
Q

What current does the mains supply?

A

Alternating Current

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2
Q

What current do batteries/cells supply?

A

Direct Current

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3
Q

In ac supplies, what is happening to the current?

A

Current is constantly changing direction

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4
Q

How alternating currents produced?

A

By alternating potential difference in which the positive and negative ends keep alternating

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5
Q

What do the UK mains supply?

A

ac around 230 V

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6
Q

What is frequency of the ac mains supply in the UK?

A

50 cycles per second or 50 Hz

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7
Q

What does direct current mean?

A

Is current that is always flowing in the same direction

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8
Q

How is direct current created?

A

By a direct potential difference

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9
Q

How most electrical appliances connected to mains supplies?

A

By three-core cables

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10
Q

What are three-core cables?

A

Means they have 3 wires inside them - each with core of copper & coloured plastic coating

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11
Q

What is the name of the blue coloured wire?

A

Neutral wire

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12
Q

Where is neutral wire found?

A

On the left of the plug

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13
Q

What does the neutral wire do?

A

Completes the circuit and carries away current (electricity normally flows out through it)

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14
Q

How many volts is the neutral wire at?

A

0 V

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15
Q

What is the name of the brown coloured wire?

A

Live wire

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16
Q

Where is the live wire found?

A

On the right of the plug

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17
Q

What does the live wire do at?

A

Provides the alternating pd from the mains supply (normally electricity flows in through it)

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18
Q

How many volts is the live wire?

A

about 230 V

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19
Q

What is the name of the green and yellow coloured wire?

A

Earth wire

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20
Q

What does the earth wire do?

A

Protects the wiring, and for safety - it stops the appliance casing from becoming live

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21
Q

Does the earth wire carry current?

A

No, doesn’t usually unless there’s a fault1

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22
Q

How many volts is the earth wire at?

A

0 V

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23
Q

Why does touching the live wire give you an electric shock?

A
  1. Your body (just like Earth) is 0 V
  2. If you touch live wire = large potential difference is produced across your body & current flows through you
  3. Causes large electrical shock = injure/kill you
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24
Q

Why is it even when the plug or light switch is turned off, there is danger of getting an electrical shock?

A
  • Current isn’t flowing but still pd in live wire

- If contact with live wire = body would provide a link between supply & earth = current would flow through you

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25
Q

Why is any connection between live and earth is dangerous?

A

If link creates low resistance path to earth = huge current will flow - result in fire

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26
Q

Describe briefly how electricity is generated from fossil fuels

A
  1. Heat is released from fuel and boils the water to make steam
  2. The steam turns the turbine
  3. The turbine turns a generator and electricity is produced
  4. The electricity goes to the transformers to produce the correct voltage
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27
Q

Why is steam used to turn the turbine and not water?

A

Steam has more energy than water

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28
Q

What are electrical applicances are designed to do?

A

Transfer energy to components in the circuit when a current flows

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29
Q

What does it mean an electrical appliance has a higher current?

A

Higher current = more energy transferred to thermal energy stores of components (& surroundings)

30
Q

What does it mean if an electrical appliance transfers more energy than another one in the same given time?

A

It has a higher power

31
Q

What does a power rating of an electrical appliance tell you?

A

Tells you maximum amount of energy transferred between stores per second when appliance is in use

32
Q

If an electrical appliance has a higher power, does this mean it transfers energy more usefully?

A

No

33
Q

How does giving electrical appliances power ratings help customers choose between models?

A

e.g. Lower power rating = less electricity an appliance uses in given time = cheaper to run

34
Q

What are potential differences?

A

Energy Transferred per Charge Passed

35
Q

When an electrical charge goes through a change in p.d., what happens?

A

Energy is transferred

36
Q

Why is energy is supplied to the charge at the power source?

A

To ‘raise’ it though a potential

37
Q

When does this charge give up this energy?

A

When it ‘falls’ through any potential drop in components elsewhere in circuit

38
Q

What will a battery with bigger pd supply and why?

A

It’ll supply more energy to circuit for every coulomb of
charge which flows round it because the charge is raised
up “higher” at the start

39
Q

What is the national gird?

A

Giant system of cables and transformers that covers UK & connects power stations to consumers

40
Q

What does the national gird do?

A

Transfers electrical power from power stations anywhere on gird (the supply) to anywhere else on the gird where it’s needed (the demand) i.e. distributes electricity

41
Q

When does the demand for electricity increase?

A
  • People get up in the morning
  • Come home from school or work
  • It starts to get dark or cold
  • Popular events like sporting final = peak in demand
42
Q

Why do power stations often run at well below their maximum power output?

A

So there’s spare capacity to cope with high demand (even if there’s an unexpected shut-down of another station)

43
Q

To transmit a huge amount of power, what is needed?

A

A high potential difference or high current is needed

44
Q

What is the problem with using a high current?

A

Problem is that loads of energy is lost as wires heat up so energy is transferred to thermal energy store of surroundings

45
Q

Why does the national grid uses high pd and low current?

A

Much cheaper to boost the pd up really high (to 400,000 V) and keep current relatively low

46
Q

For a given power, what does increasing the pd do to the current?

A

Increasing the pd decreases the current which decreases energy lost by heating wire and surroundings - makes the national grid an efficient way of transferring energy

47
Q

What does the national grid require to get pd to 400 000 V to transmit power?

A

Requires transformers & big pylons with huge insulators

48
Q

What do transformers have to do to the pd?

A

Have to step pd up at 1 end, for efficient transmission, & then bring it back down to safe, usable levels at other end

49
Q

How is pd increased?

A

It’s (‘stepped up’) using a step-up transformer

50
Q

How is pd decreased?

A

It’s (‘stepped down’) using a step-down transformer

51
Q

What is the build-up of static caused by?

A

Caused by friction

52
Q

What happens when certain insulating materials are rubbed together?

A
  • Negatively charged electrons will be scraped off one and dumped on other
  • This will leave materials electrically charged, with a positive static charge on one & an equal negative static charge on the other
53
Q

What happens when a polythene rod is rubbed with a cloth duster?

A

Electrons move from the duster to the rod

54
Q

What happens when an acetate rod is rubbed with a cloth duster?

A

Electrons move from the rod to the duster

55
Q

How are both positive (+ve) and negative (-ve) electrostatic charges produced?

A

By the movement of electrons

56
Q

Do positive charges move?

A

NO

57
Q

What is a positive charge caused by?

A

Caused by electrons moving away elsewhere

58
Q

What happens the material loses electrons?

A

Material loses the electrons, loses some negative charge = left with an equal positive charge

59
Q

How are sparks created?

A
  • As electric charge builds on an object = pd between object and earth (which is at 0 V) increases
  • If pd gets large enough = electrons can jump across gap between charged objects and earth = this is the spark
60
Q

Why can you get a static shock when getting out of car?

A
  • Sparks can jump to any earthed conductor that’s nearby
  • A charge builds up on car’s metal frame, and when you touch car, charge travels through you to earth (usually happens when gap if fairly small)
61
Q

What is lightning essentially?

A

A really big spark

62
Q

When 2 electrically charged objects are brought close together what happens? What are these forces do and what are they known as?

A
  • They exert a force on one another
  • These forces will cause objects to move if they’re able to = known as electrostatic attraction/repulsion & is non-contact force
63
Q

If you suspend a rod with known charge from piece of

string, and place an object with same charge nearby it, what will happen?

A

It will repel the rod

64
Q

If you suspend a rod with known charge from piece of

string, and place an oppositely charged object nearby it, what will happen?

A

Will cause rod to move towards the object

65
Q

What does an electrically charged object create?

A

An electric field

66
Q

When a charged object is placed in electrical field of another object, what happens and what is caused by?

A

It feels a force (that causes attraction or repulsion) caused by electric fields of each charged object interacting with each other

67
Q

What does isolated mean?

A

It’s not interacting with anything

68
Q

Describe how sparking can be explained by electric fields

A
  1. Sparks are caused when there’s a high enough pd between a charged object and the earth (or earthed object)
  2. A high pd = strong electric field between charged object & earthed object
  3. Strong electric field = electrons in air particles to be removed (known as ionisation)
  4. Air is normally an insulator, but when ionised it much more conductive = so current can flow through it → this is the spark
69
Q

Name 3 things to bare in mind when drawing electric fields?

A
  • Electric field lines go from positive to negative
  • They’re always at a right angle to surface
  • The closer together the lines are = stronger the field is
70
Q

State the units for equation E = QV (Energy transferred = Charge flow x Potential Difference)

A

Energy transferred = J
Charge flow = C
Potential Difference = V

71
Q

State the units for equation P = VI (Power = Potential Difference x Current)

A

Power = W
Potential Difference = V
Current = A

Physics 9-1 iGCSE Oxford AQA (12 decks)

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