2.5 Mains Electricty

Question 1

What is direct current?

Answer 1

Current that passes round a circuit in one direction

Question 2

What is direct current produced by?

Answer 2

Batteries
Power supplies
Solar cells

Question 3

What is alternating current?

Answer 3

The current passes in one direction then reverses and passes in the other direction (constantly changing direction)

Question 4

What type of current is the mains supply?

Answer 4

Alternating current

Question 5

What is the frequency of the mains supply?

Answer 5

50Hz

Meaning it changes direction 50 times per second

Question 6

What is the voltage of the mains supply?

Answer 6

230V

Question 7

What can you calculate from an oscilloscope trace diagram?

Answer 7

Frequency

Question 8

On a 3 pin plug what is the cover made from and why?

Answer 8

Plastic

It is a good insulator

Question 9

On a 3 pin plug what are the pins made from and why?

Answer 9

Brass
Good conductor
Will not rust

Question 10

On a 3 pin plug what is the blue wire?

Answer 10

Calming therefore:

Neutral

Question 11

On a 3 pin plug what is the Brown wire?

Answer 11

Chocolate (lively) therefore:

Live

Question 12

On a 3 pin plug what is the yellow green/wire?

Answer 12

Natural therefore:

Earth

Question 13

Which wire does a two core cable not have?

Answer 13

An earth wire

Question 14

Why do appliances with metal have to be earthed?

Answer 14

To prevent electric shocks

Question 15

Why does a plastic casing not need earthing?

Answer 15

It is double insulated

Question 16

What does a fuse do?

Answer 16

A thin piece of wire that will melt and break if too large a current flows through it

Question 17

How does a fuse melt?

Answer 17

The more current the hotter the thin wore will become causing it to melt

Question 18

What is the benefit of having a fuse?

Answer 18

It prevents further damage to the appliance or user

Question 19

What is an RCCB?

Answer 19

Residual current circuit breaker

Question 20

What does an RCCB do?

Answer 20

Compares the current entering the live wire with the current leaving the neutral wire

And if the current is too great it will disconnect the current in the live wire

Question 21

What is the benefit of a RCCB over a fuse?

Answer 21

It is much faster

Question 22

What is the waste energy in a filament bulb?

Answer 22

Heat

Question 23

Name a bulb where less energy is wasted?

Answer 23

Compact fluorescent lamps (CFL’s)

Question 24

To get the best electrical appliance what features should you look for?

Answer 24

The most powerful and efficient in transferring energy

Question 25

What energy is transferred to a resistor and what is the result of this?

Answer 25

Electrical energy

The resistor heats up

Question 26

What electrical issues can occur?

Answer 26

Damage to sockets, plugs, cables or appliances
Overloading sockets leading to fires from over heating
Electric shocks if brought near water