Why do we need to know the power of electrical appliances?

Electrical appliances transform energy. The power of an electrical appliance is the rate at which it transforms energy. Most appliances have their power and the potential difference of the supply they need printed on them. From this we calculate their current and the fuse they need.

Current and Charge
Electric current is the rate of flow of charge.
When an electrical charge flows through a resistor, electrical energy is transformed into heat energy.
 

Power
The rate at which energy is transformed in a device is called the power.

You will have to use this equation to calculate what current flows through a device then us this information to choose what fuse to put in its plug.

e.g. A 3 kW kettle is connected to the 240V mains.

a) What current does it draw?        C = P / V = 3000 / 240 = 12.5A

b) Should there be a 1A, 5A, 15A or 30A fuse in its plug?     The next fuse above 12.5 is 15A
 

Higher Tier Stuff

e.g. A current of 7A flow through a food mixer connected to the 240V mains.

a) How much charge flows through it in 5 minutes?     Ch = C x t    = 7 x (5 x 60) =   2,100C

b) How much electrical energy does it transfer?       E.T. = V x C   =   240 x 2,100   = 504,000J     ( = 504 kJ)

c) Calculate its power.        P = E.T. / t  = 504,000 / (5 x 60)  = 1,680W  ( = 1.68 kW)        or  P = V x C  = 240 x 2,100 = 1,680W