Power of an electrical appliance 

• Power of an electrical appliance is the rate at which it transforms electrical energy..

• Power is measured in Watts (W).

    Cost of electricity

• The electricity meter shows the number of kilowatt-hours used since it was last read.

• The number of Kilowatt-hours is the amount of energy transferred from the mains.

      Energy transferred    =    Power      x     time 

           kilowatt-hour             kilowatt          hour
              kWh                       kW               h

• The electricity bill refers to kilowatt-hour as a unit.

• The amount of electrical energy a device transforms depends on how long the appliance is
  
  switched on and the rate at which the device transforms energy.

• The cost of energy transferred from the mains is given by the following formula: