P2.4 Using mains electricity

Question 1

Mains electricity

Answer 1

Mains electricity is an a.c. supply. In the UK it has
a frequency of 50 cycles per second (50 hertz)
and is about 230 V.
d) Most electrical appliances are connected to the
mains using cable and a three-pin plug.

Question 2

Direct current

Answer 2

If the current flows in only one direction it is called direct current (DC).on an oscilloscope the wave is straight.

Question 3

alternating current

Answer 3

If the current constantly changes direction, it is called alternating current (AC).on an oscillascope the wave is wavy.

Question 4

describe the structure of a cable

Answer 4

A mains electricity cable contains two or three inner wires. Each has a core of copper, because copper is a good conductor of electricity. The outer layers are flexible plastic, because plastic is a good electrical insulator. The inner wires are colour coded:
Colours of inner wires within a cable
Colour	Wire
blue	neutral
brown	live
green and yellow stripes	earth

Question 5

Fuses

Answer 5

The fuse breaks the circuit if a fault in an appliance causes too much current flow. This protects the wiring and the appliance if something goes wrong. The fuse contains a piece of wire which melts easily. If the current going through the fuse is too great, the wire heats up until it melts and breaks the circuit

Question 6

what materials are usually earthed.

Answer 6

Appliances with metal cases are usually earthed.
Many electrical appliances - including cookers, washing machines and refrigerators - have metal cases. The earth wire creates a safe route for the current to flow through if the live wire touches the casing.
A strong current surges through the earth wire because it has a very low resistance. This breaks the fuse and disconnects the appliance.

Question 7

Double insulation

Answer 7

As a result, the casing cannot give an electric shock, even if the wires inside become loose. These appliances have double insulation and carry a symbol

Question 8

Power

Answer 8

Power is a measure of how quickly energy is transferred. The unit of power is the watt, W.
The more energy that is transferred in a certain time, the greater the power. A 100 W light bulb transfers more electrical energy each second than a 60 W light bulb

Question 9

Calculating power

Answer 9

Calculating power
You can work out power using this equation:
P = E ÷ t
P is the power in watts, W
E is the energy transferred (or work done) in joules, J
T is the time in seconds, s