Chapter 5 - Mains Electricity Flashcards Preview

Physics - Additional > Chapter 5 - Mains Electricity > Flashcards

Flashcards in Chapter 5 - Mains Electricity Deck (16)
Loading flashcards...
1
Q

What supplies direct current

A

Cells and batteries

2
Q

What is alternating current

A

The current from the mains supply passes in one direction, then reverses and passes in the other direction

3
Q

What is the frequency of the U.K. mains supply and what does it mean

A

50 Hz. This means it chances direction 50 times each second

4
Q

What is the voltage of the mains

A

230 v

5
Q

Why is the outer cover of the three pin plug made of plastic.

A

It’s a good electrical insulator

6
Q

Why are the pins of the plug made of brass

A

Brass is a good electrical conductor. It is also hard and will not rust or oxidise

7
Q

What is the brown wire connected to

A

The live pin.

8
Q

What is the blue wire connected to

A

The neutral pin

9
Q

What is the green and yellow wire connected to

A

The earth pin

10
Q

Why do appliances with metal cases need to be earthed but appliances with plastic cases do not

A

If a fault develops, and the live wire touched the metal case, the becomes live and could give a shock to anyone who touches it. Plastic is an insulator and cannot become live

11
Q

What is the purpose of a fuse

A

A fuse contains a thin wire that heats up and melts if too much current passes through it which cuts off the current.

12
Q

Why should the rating of the fuse be slightly higher than the normal working current of the appliance

A

So that it melts at the correct time. If it is much higher, it will not melt soon enough. If it is not higher than the normal current, it will melt as soon as the appliance is switched on

13
Q

What is a circuit breaker

A

Something that is used in place of a fuse. It’s an electromagnetic switch that opens and cuts off the supply if the current is bigger than a certain value

14
Q

What does a residual current circuit breaker do and what are its advantages

A

It cuts off the current in the live wire if it is different to the current in the neutral wire. It works faster than a fuse or ordinary circuit breaker

15
Q

Why are filament bulbs very inefficient

A

Doesn’t last as long as a low energy bulb

16
Q

What is direct current

A

The current that passes round the circuit in one direction