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AQA Physics GCSE > Electricity - electricity in homes > Flashcards

Electricity - electricity in homes Flashcards

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1
Q

what are the two types of current

A

alternating ( changes direction) and direct (one direction)

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2
Q

what type of current is in UK plug sockets

A

alternating

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3
Q

what is the frequency and voltage of UKs main electricity supply

A

50HZ 230V

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4
Q

examples of direct currents

A

batteries and cells

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5
Q

what colour is the live wire

A

brown

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6
Q

what are the three types of wires in appliances

A

live wire, neutral wire and earth wire

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7
Q

Describe the live wire

A
  • carries 230V potential
  • It provides the alternating voltage from the mains electricity supply.
  • connected to a fuse in the plug
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8
Q

what colour is the neutral wire

A

blue

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9
Q

describe the neutral wire

A
  • at or close to earths potential ( 0V )
  • completes the circuit
  • carries current away from appliance
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10
Q

what colour is the earth wire/ safety wire

A

green and yellow striped

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11
Q

describe the earth wire

A
  • has 0V potential
  • only carries current if there is a fault
  • is a safety wire to stop the appliance from becoming live
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12
Q

energy transferred =

A

power x time
charge x potential difference

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13
Q

why will a 50W bulb use 50J of energy per second

A

because Joules are equal to watts

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14
Q

what is the national grid

A

the network of cables and transformers that connect power stations with houses and shops in the UK

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15
Q

What are power stations and what do they do

A
  • buildings which create an electric current, which is an energy carrier
  • Power stations produce electricity at a voltage of 25,000 Volts.
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16
Q

why are bigger power stations more efficient than smaller

A
  • they can burn lots of fuel at high temperatures and this will create hot steam that’ll turn the turbines, and these are more efficient and higher temperatures
17
Q

what do step up transformers do

A

increase voltage from 25,000 to 400,000V, causing the current to decrease.

This reduces the current and this reduces how much heat is lost when it’s being transported across the country.
This increases the efficiency of the National Grid system.

18
Q

what do step down transformers do

A

To get electricity to a safer voltage (230 Volts) in our homes, step-down transformers reduce the voltage to a lower value.

19
Q

what do fuses and circuit breakers do

A

protect us from electrical appliances by stopping the flow of electric current flow if it gets too high.

20
Q

what are circuit breakers

A
  • special devices that switch off the flow of current if the current is higher than a certain value.
  • do the same job as fuses but can be used lots of times.
21
Q

what are fuses

A
  • contain a thin wire that melts if the current flowing through an appliance is too high.
    This breaks the circuit and stops the flow of electric current.
  • can only be used once, must be replaced after
22
Q

why are circuit breakers better than fuses

A
  • circuit breakers break the circuit faster, reducing the risk of electric shock
  • circuit breakers can be used more than once
23
Q

what do fuse ratings do

A

they tell you the level where a fuse will begin to melt

24
Q

how should you choose a fuse

A

The fuse chosen should have a value just above the normal current that an electrical appliance uses.
e.g - if the operating current is 3.9 A, and fuses with values of 3 A, 5 A or 13 A are available, the most suitable fuse is the 5 A fuse.

25
Q

Why is a 13 A fuse wrong to use for an appliance with a 3.9 A operating current

A

More than three times the normal operating current is needed to melt the fuse.
Therefore, the 13 A fuse might not melt even if the appliance developed a fault

26
Q

what will happen if you touched a faulty appliance with a metal casing

A

you will get an electric shock, metal conducts electricity and if the live wire touches the casing and you touch it, you’ll receive an electric shock

27
Q

describe what the earth wire would do if an appliance was faulty

A

An earth wire is a low resistance wire that connects the metal case to the ground.
If the casing is touched by a wire inside the appliance, the current will flow through the earth wire.
Because the resistance of the earth wire is low, a very high current will flow through it, breaking the fuse in the device. This will stop the flow of current and make the appliance safe.

28
Q

why can the live wire and the earth wire never be in contact

A
  • would remove the safety feature of the earth wire.
  • would also take a huge amount of current, which would overpower the fuse.
  • fuse would melt and could explode.
29
Q

why might the live wire still be dangerous when it’s switched off ( e.g light switch off)

A

because it could still be holding a potential difference

30
Q

what is an electric shock

A

where if you touched the live wire, your body would supply a link between the supply and the ground, could kill you

31
Q

power equation

A

power =e/t

32
Q

what does the amount of energy an appliance transfers depend on

A
  • how long its switched on
  • power of the appliance
33
Q

what would happen if someone touched the live wire

A
  • our body is at 0V, live wire is 230V
  • Touching the live wire makes a large pd produce across your body, causing a current to flow through you
  • This causes a large electric shock which could injure or kill you
34
Q

how can we reduce energy loss in the national grid

A

by building power stations nearer to homes

35
Q

why do the step up transformers increase the voltage

A

because less energy is lost in the cables when pd is very high
- using a high current makes energy get lost from the wires
- for a given power, increasing pd decreases current, which decreases energy lost

36
Q

advantages of ac over dc

A
  • easy to use a transformer to increase ot decrease pd
37
Q

how can the earth wire stop someone getting an electric shock

A
  • earth wire is connected into the ground with a metal rod
  • if the case becomes live, huge current flows into the earth, causing the fuse to melt and shut off the current
  • preventing anyone from getting an electric shock
38
Q

why is the importance of step up transformers

A
  • boosts pd
  • lowers current
  • less energy lost through the thermal store through the wires

AQA Physics GCSE (38 decks)

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