Electrical Power

These figures tell you how POWERFUL the appliance is. How much electrical energy it uses in a second. In other words the RATE at which electrical energy is converted to other forms.

In one second the 100W light bulb uses 100 J of electrical energy and converts some of it into light energy.
However in one second the immersion heater uses 3 kW (3000 W) of electrical energy and converts it into heat energy.



We know that electrical energy is given by the equation:

Energy = Voltage x Current x Time = Voltage x Charge

And so:
Power = Energy converted/ Time = Voltage x Current x Time/Time = Voltage x current

The formula for electrical power is:


[Power is measured in watts with current in amps and voltage in volts].

For large amounts of power we use kilowatts kW (1 kW = 1000 W) and megawatts (1 MW = 1000 000 W). A large power station will operate at over 1000 MW!


Using Ohm's law (V = IR) we can derive two alternative versions of the power equation: