Domestic electricity - Paper 1

Question 1

State the typical voltage for mains electricity?

Answer 1

230 V

Question 2

State the frequency of mains electricity

Answer 2

50 Hz

Question 3

Define a.c.

Answer 3

Alternating current, the electrons vibrate backwards and forwards. Mains electricity use a.c.

Question 4

Define d.c.

Answer 4

Direct current. Electrons only flow in one direction. This is what we get from batteries

Question 5

State the names and colours of the 3 wires found inside a cable.

Answer 5

Live wire - Brown
Neutral wire - Blue
Earth wire - Green and yellow stripes

Question 6

Which wire can be missing from some appliances? Why?

Answer 6

Earth wire, if the appliance is plastic and you cannot get an electric shock from it.

Question 7

State the role of the line wire

Answer 7

To carry the alternating potential difference from the supply to the component. the potential difference between the live and the earth is 230 V

Question 8

State the role of the neutral wire

Answer 8

The neutral wire complete the circuit from the component back to the supply. The neutral wire is at or close to 0V

Question 9

State the role of the Earth wire.

Answer 9

It is a safety wire to stop an appliance becoming live. the earth wire is at 0V as it only carries a current if there is a fault.

Question 10

State the relationship between power, potential difference and current.

Answer 10

Power = potential difference x current
P = VI

Question 11

State the units of power

Answer 11

Watts (W)

Question 12

State the units of potential difference

Answer 12

Volts (V)

Question 13

State the units of current

Answer 13

Amperes (A)

Question 14

State the relationship between power, resistance and current.

Answer 14

Power = (Current)squared x resistance

Question 15

State the units for resistance

Answer 15

Ohms

Question 16

When using an electrical device what factors affect how much electrical energy it uses?

Answer 16

1. Time it is used for

2. The power of the appliance

Question 17

State the equation between energy transferred, power and time

Answer 17

Energy transferred (J) = Power (W) x time (s)

Question 18

State the equation between energy transferred, charge and potential difference

Answer 18

Energy transferred (J) = Charge (C) x potential difference (V)
E = QV

Question 19

State the parts that make up the national grid

Answer 19

Cables, pylons, step up transformers, step down transformers

Question 20

What does a step up transformer do? Why?

Answer 20

Increases the potential difference, which decreases the current. this reduced the amount of energy lost os heat so makes them more efficient.

Question 21

What does a step down transformer do? Why?

Answer 21

Decreases the potential difference which increases the current. this makes them safer to use

Question 22

What is the casing of a plug made from? Why?

Answer 22

Plastic , it is a good insulator and strong

Question 23

What are electrical wires made from? Why?

Answer 23

Copper, ductile and a good conductor

Question 24

What are the pins in a plug made from? Why?

Answer 24

Brass, its a good conductor but also strong

Question 25

Where is the fuse in a plug?

Answer 25

Between the live pin and the live wire

Question 26

What is the role of the fuse?

Answer 26

If current gets too high the fuse melts and breaks the circuit, cutting off the live wire

Question 27

What happens when the live wire touches the case, in terms of the earth wire?

Answer 27

The large current surges down the earth wire and the fuse blows