4-Mains Elecricity & Electrical Appliances Flashcards Preview

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Flashcards in 4-Mains Elecricity & Electrical Appliances Deck (23)
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0
Q

What is alternating current (a.c.)?

A

A current that changes direction or flow back and forth continuously. The number of complete cycles if reversal per second is the frequency.

1
Q

What is a direct current (d.c.)?

A

A current that always flows in the same direction. Eg. Cells and batteries.

2
Q

What is the frequency of UK mains electricity?

A

50 Hertz.

3
Q

What is the voltage of UK mains supply?

A

230 volts.

4
Q

How are most electrical appliances connected to the mains electricity supply?

A

Using a cable and three pin plug.

5
Q

What colour is the earth wire?

A

Green and yellow.

6
Q

What colour is the live wire?

A

Brown.

7
Q

What colour is the neutral wire?

A

Blue.

8
Q

Why are the inner cores of wires made of copper?

A

It’s a good conductor.

9
Q

Why are the outside of wires made of flexible plastic?

A

It’s a good insulator.

10
Q

Why are the pins of a plug made of brass?

A

It’s a good conductor.

11
Q

What is the x-axis of an oscilloscope graph?

A

Time.

12
Q

What is the y-axis of an oscilloscope graph?

A

Voltage.

13
Q

How does a RCCB (residual current circuit breaker) work?

A
  1. Current becomes too high.
  2. RCCB trips switch.
  3. Circuit is broken.
  4. Cable or appliance is protected.
14
Q

What does a RCCB do?

A

Detects the difference between live and neutral wires which shouldn’t be there.

15
Q

How does a fuse work?

A
  1. Current larger than current rating of fuse.
  2. Fuse wire melts.
  3. Circuit broken.
  4. Cable or appliance is protected.
16
Q

What is a fuse?

A

A short, thin piece of wire with a low melting point.

17
Q

How does the earth wire work?

A
  1. Live casing.
  2. Short circuit.
  3. Current surges to earth.
  4. Fuse wire melts.
  5. Circuit is broken.
  6. Cable or appliance protected.
18
Q

What appliances need to be earthed?

A

Ones with metal casing.

19
Q

Why does the current ‘flow to earth’?

A

The earth wire offers the least resistance.

20
Q

What is current?

A

The rate of flow of charge.

21
Q

What is charge measured in?

A

Coulombs (C).

22
Q

What is the relationship between potential difference and charge?

A

The greater the potential difference, the more energy transferred by every coulomb of charge.