The more energy that is transferred in a certain time, the greater the power. A 100W light bulb transfers more electrical energy each second than a 60W light bulb.
The equation below shows the relationship between power, potential difference (voltage) and current:
power (watts) = current (amps) x potential difference (volts)
We can calculate the amount of electrical energy transferred by an appliance and how much it costs to run. This is useful for comparing the advantages and disadvantages of using different electrical appliances for a particular purpose.
Electrical energy calculations
The amount of electrical energy transferred to an appliance depends on its power and the length of time it is switched on. The amount of mains electrical energy transferred is measured in kilowatt-hours, kWh. One unit is 1 kWh.
E = P × t
The equation could be written
E=Current x Volts x time
E = Vx I x t
E is the energy transferred in a second
P is the power in Joules
T is the time in seconds
V= voltage in volts
I = current in amps