Section 2 b) Summary

Mains electricity is the electricity supplied to each home. In the UK it is a.c. and 230V. A.c. means alternating current: it is constantly changing. By contrast, d.c. means direct current and does not change direction. This can be found in cell or battery powered circuits.

Current flowing though a circuit causes resistance. This can be calculated with the following formula:

Voltage = Current x Resistance
V= I R
(Remember this by calling it VIR pronounced veer)

Resistance causes a heating effect due to energy transfer. This increase in temperature also increases the resistance. This is used to our advantage in a variety of domestic situations

• Fuses melt when the current is too high because it causes resistance and heating
• Toasters toast bread with coils of high resistance wires that heat up
• Kettles can heat water with a high resistance coil in the bottom of the appliance. 

Fuses and circuit breakers are chosen based on the current that should flow through the appliance with normal use. Fuses generally come in 3A, 5A, 7A and 13A. An appliance that would usually have a current of 2.3A flowing would use a 3A fuse, for example. 

Appliances are usually rated on power and voltage, so to calculate the necessary fuse we need to find out the current through this formula:

Power = Voltage x Current
P = I V
(Remember it by calling it PIV like pivot)

So an appliance with a rating of 1000W and 240V would be
1000 / 240 = 4.17 A
So we should use a 5 A fuse. 

Another important formula to know is this:

Energy transferred = Voltage x Current x Time
E = V I T
(Remember it by calling it EVIT like eviter, to avoid, in French)


Electrical circuits come with hazards that can cause injury or damage:

But there are often safety features put in place to ensure we are not hurt: