Current, charge, power and fuses

Current, charge, power and fuses

Physics GCSE science revision- Electricity

Electrical appliances transfer energy but some transfer energy better than others.

Simply walking into an electrical goods store and you’ll see how much choice people have today when choosing a new appliance. However, not all are very efficient at transferring energy. A good comparison is filament lamps and energy-saving lamps, like LED’s.

Filament lamps are composed of a thin metal filament. When electricity is passed through the filament it glows red hot. Instead of most electrical energy being transferred into light energy most is lost as heat energy.

Energy-saving lamps, however, transfer most electrical energy into light energy as opposed to heat energy. This means that far less energy is ‘wasted’ as heat.



Physics GCSE science revision- ElectricityPower refers to how fast energy is transferred. It’s measured in watts (W). The more energy that’s transferred within a particular time the more the power. For example, a 60 W bulb transfers less electrical energy each second than a 100 W bulb.

Power can be calculated by using the following equation:

P = E / t

  • P is the power in watts (W)
  • E is the energy that’s transferred in joules (J)
  • t is the time in seconds (s)

The power coming from an electrical appliance can be worked out by using the current flowing through it and the potential difference across it. In that case you can use this equation:

P = I x V

  • P is the power in watts (W)
  • I is the current in amps (A)
  • V is the potential difference in volts (V)

If you’re asked in you exam for the current when you know the potential difference and power then you can rearrange the equation:

I = P / V



Physics GCSE science revision- ElectricityAs you may have already realised, the purpose of the fuse is to protect both an appliance and the electrical circuit.

When too much current is flowing through an appliance the fuse will break. A fuse consists of a little piece of wire which melts very easily if it gets too hot. So, if the current is too much the wire heats up and melts which breaks the circuit.

Fuses come in a number of standard ratings, the most common being 3 A, 5 A and 13 A. The fuse in a component is a little higher than the current required by the appliance. For example, a 5 A fuse would be used inside an appliance which works at 3 A.