Electrical power

-The more powerful an applience, the faster the rate at which it transfers energy 

-We measure the power of an appliance in watts (W) or kilowatts (kW)

- 1 watt is a rate of transfer of energy of 1 joule per second (J/s)

- 1 kilowatt is equal to 1000 watts 

-You calculate power using;

 P= E/t 

Where;

• P is the power in watts, W 
• E is the energy transferred to the appliance in joules , J
• t is the time taken for the energy to be transferred in seconds, s 

For any appliance 

-Its useful power out (or output power) is the useful energy per second transferred by it 

-Its total power in (or input power) is the energy per second supplied to it 

Efficiency = useful power out       (x100%)

                     total power in