P2 Electricity in the Home (page 186)

Question 1

There are two types of electricity supply, what are they?

Answer 1

alternating current (ac) and direct currents (dc)

Question 2

What is ac supplies?

Answer 2

the current is constantly changing direction.

Question 3

Alternating currents are produced by what voltages?

Answer 3

alternating voltages, in which the positive and negative ends keep alternating.

Question 4

What current is the UK mains supply (the electricity in your home)?

Answer 4

it is an ‘ac’ supply at around 230 V.

Question 5

What is the frequency of the ac mains supply?

Answer 5

it is 50 cycles per second or 50 Hz (hertz)

Question 6

what supplies direct current (dc)?

Answer 6

contrast, cells and batteries supply direct durrent.

Question 7

What is Direct Durrent (dc)?

Answer 7

direct current is a current that is always flowing in the same direction.

It is created by direct voltage.

Question 8

How many cables do most cables have?

Answer 8

most cables have three separate wires.

Question 9

How are most electrical appliances connected to the mains supply?

Answer 9

they are mostly connected by three-core cables. (this means they have three wires inside them, each with a core of copper and a coloured plastic coating).

Question 10

The colour of the insulation on each cable shows what?

Answer 10

it shows its purpose.

Question 11

Why are the separate wires of the cable always the same colour for every appliance?

Answer 11

This is so that it is easy to tell the different wires apart.

Question 12

What are the colours of the three wires in most appliances?

Answer 12

Brown
Blue
Green & Yellow

Question 13

What do the brown wire represent on a cable, and what type of electricity supply is it?

Answer 13

the brown wire is the Live Wire.

The live wire provides the alternating potential difference (at about 230 V from the mains supply)

Question 14

What do the Blue wire represent on a cable, and what type of electricity supply is it?

Answer 14

The blue wire is the Neutral Wire.

The neutral wire completes the circuit - when the appliance is operating normally, current flows through the LIVE and NEUTRAL wires, it is around 0 V.

Question 15

What do the Green & Yellow wire represent on a cable, and what type of electricity supply is it?

Answer 15

The green & yellow wire is the Earth Wire.

It is for protecting the wiring, and for safety - it stops the appliance casing from becoming live. It doesn’t usually carry a current - only when there’s a fault. its also at 0 V.

Question 16

Can the Live Wire (brown) give you an electric shock, and why?

Answer 16

Yes it can.

Like our body, (it’s just like the earth) is at 0 V. This means that if you touch the live wire, a large potential difference is produced across your body and a current flows through you.

Question 17

If a current flows through you, what do this mean?

Answer 17

this causes a large electric shock which could injure or even kill you.

Question 18

Is it dangerous if a plug socket or a light switch is turned off (i.e. the switch is open)?

Answer 18

Yes it is still a danger, of an electric shock. A current isn’t flowing but there’s still a pd (potential difference) in the live wire. If you made contact with the live wire, your body would provide a link between the supply and the earth, so a current would flow through you.

Question 19

Any connection between live and earth can be dangerous, why?

Answer 19

If the link creates a low resistance path to earth, a huge current will flow, which could result in a fire.

Electricity is very useful, but it can also be very dangerous. Make sure you know the risks.

Question 20

State the potential difference of:

a) the live wire
b) the neutral wire
c) the earth wire

Answer 20

a) 230 V
b) 0 V
c) 0 V