4-Mains Elecricity & Electrical Appliances

Question 0

What is alternating current (a.c.)?

Answer 0

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

Question 1

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

Answer 1

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

Question 2

What is the frequency of UK mains electricity?

Answer 2

50 Hertz.

Question 3

What is the voltage of UK mains supply?

Answer 3

230 volts.

Question 4

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

Answer 4

Using a cable and three pin plug.

Question 5

What colour is the earth wire?

Answer 5

Green and yellow.

Question 6

What colour is the live wire?

Answer 6

Brown.

Question 7

What colour is the neutral wire?

Answer 7

Blue.

Question 8

Why are the inner cores of wires made of copper?

Answer 8

It’s a good conductor.

Question 9

Why are the outside of wires made of flexible plastic?

Answer 9

It’s a good insulator.

Question 10

Why are the pins of a plug made of brass?

Answer 10

It’s a good conductor.

Question 11

What is the x-axis of an oscilloscope graph?

Answer 11

Time.

Question 12

What is the y-axis of an oscilloscope graph?

Answer 12

Voltage.

Question 13

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

Answer 13

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

Question 14

What does a RCCB do?

Answer 14

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

Question 15

How does a fuse work?

Answer 15

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

Question 16

What is a fuse?

Answer 16

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

Question 17

How does the earth wire work?

Answer 17

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

Question 18

What appliances need to be earthed?

Answer 18

Ones with metal casing.

Question 19

Why does the current ‘flow to earth’?

Answer 19

The earth wire offers the least resistance.

Question 20

What is current?

Answer 20

The rate of flow of charge.

Question 21

What is charge measured in?

Answer 21

Coulombs (C).

Question 22

What is the relationship between potential difference and charge?

Answer 22

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