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SHHS - Science - Physics GCSE 2018on > 10. P5 Mains Electricity > Flashcards

10. P5 Mains Electricity Flashcards

1
Q

What is meant by the frequency of an AC supply?

A

The number of cycles per second.

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2
Q

What is the frequency of mains electricity in the uk?

A

50 Hz (50 cycles per second)

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3
Q

What two wires do every device connected to the mains have?

A

Live wire and neutral wire

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4
Q

What type of current is the mains electricity?

A

A.C. (alternating current)

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5
Q

Potential Difference of the mains supply?

A

230 V

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6
Q

Maximum value that the PD reaches in the mains supply of the UK?

A

325V

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7
Q

What type of current is produced by a battery?

A

Direct current

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8
Q

Describe what is meant by a direct current?

A

Current flows only in one direction only.

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9
Q

What does a fuse do in a plug?

A

Protects the user, melts if too high a current flows through it, breaking the circuit.

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10
Q

What colour is the live wire?

A

Brown

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11
Q

What colour is the neutral wire?

A

Blue

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12
Q

5 safety features of a 3 pin plug?

A

Fuse, Earth wire, Cable grip, colour coded wires, hard plastic coating.

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13
Q

What devices in the UK require an earth wire?

A

Devices with a metal casing.

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14
Q

What colour is the earth wire

A

Green and yellow (stripes)

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15
Q

How does the earth wire protect the user?

A

Earth wire is connected to the casing. If fault develops making the casing live, the earth wire provides a route back to socket.

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16
Q

If a current does flow down the earth wire what else happens to protect the user/device?

A

Earth wire has low resistance so large current flows and fuse melts to break circuit.

17
Q

What type of metal are the pins on a plug made out of and why?

A

Brass - good conductor and is a strong metal. Also doesn’t rust or oxidise.

18
Q

Some wires with in the house are thicker than others, why are thicker wires required sometimes? (wall sockets wires are thicker than the lighting wires)

A

Some devices require a higher current, thicker wires have less resistance and so thicker wires reduce the amount the wires heat up.

19
Q

What happens when an electric current passes through a resistor?

A

The energy supplied to the resistor causes it to heat.

20
Q

What is the national grid?

A

A system of cables and transformers, which transfer electrical energy around the country.

21
Q

Why is it important for mains electricity to be A.C. when wanting to transport it through the national grid?

A

Transformers only work with AC supplies.

22
Q

What does a step down transformer do?

A

Reduces the potential difference of the supply(for safety) which increases the current.

23
Q

What is a step up transformer used for in the national grid?

A

Increases the potential difference which decreases the current ( lower current less energy wasted).

24
Q

What appliances would only have a two core cable attached to them?

A

Appliances with a plastic casing.

25
Q

How does a circuit breaker differ from a fuse?

A

Both switch off the circuit if too much current flows, but a circuit breaker can be reset.

26
Q

Which wire is brown ?

A

The live wire

27
Q

When would you only expect the earth wire to carry a current in it?

A

If a fault caused the live wire to become connected to the metal casing in a device.

28
Q

What is current measured in?

A

Amps (A)

29
Q

What is potential difference measured in?

A

Volts (V)

30
Q

What is charge measured in?

A

Coulombs (C)

31
Q

What is power measured in?

A

Watts (W)

32
Q

What is energy measured in?

A

Joules (J)

33
Q

What is the equation linking energy, power and time?

A

Power (W) = Energy(J) /time (s)

34
Q

What is the equation linking power, current and PD?

A

Power = Voltage x Current

35
Q

What is the equation linking Voltage (PD), energy and charge?

A

Energy = Charge x Voltage

36
Q

What is the equation linking power, current and resistance?

A

P = (Current)2 x Resistance

37
Q

What is the symbol for a fuse?

A

..

SHHS - Science - Physics GCSE 2018on (16 decks)

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