Electrical Energy

* Electrical appliances can transfer electrical energy into useful energy at the flick of a switch

* An electrical appliance is designed for a particular purpose and should waste as little energy as possible 

* Power is rate of transfer of energy 

* Unit of power is Watt

 P=E/t

P- Power, W (watts)   E- Energy, J (joules)   t- time taken for energy to be transferred, s (seconds)  

Efficiancy = useful power out DIVIDED BY total power in                           (X 100%)  

* The kilo-watt hour is the enefy supplied to a 1kW appliance in 1 hour.

 E = P X t

E- energy transferred, kWh (kilowatt hours)  P- power of the appliance, kW                 t- time taken for energy to be transferred, hours

*Cost of electrical energy

Total cost = number of kWh X cost per kWh

* Cost effectiveness means getting the best value for money

* To comparethe cost effectivness of different appliances, we need to take into consideration the number of different costs

* Payback time is the time is takes for an appliance or installation to pay for itself in terms of energy savings