Electrical Energy

Every electrical appliance can waste energy in some way; usually by heating the untargeted parts of an appliances, or sound energy. E.g:

Electrical heater: heat, light from the glowing element

Toaster: heating the toast, heating the toaster itself, wire and surroundings

Hairdryer: KE of the fan and heating the filament/ anything inside the fan, sound and heating the hairdryer itself

Computer disc: energy stored in magnestic dots on the disc, energy heating the motor that drives the disc

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

Power is the rate at which energy is transferred.

The more powerful an appliance, the fater the rate at which energy transfers

W = J/s, P = E/t

1 KW = 1000 W, 1 MW = 100,000 W

The energy needed to lift a weight of 1 N 1m off the ground is 1 J

So to calculate the energy needed to lift 30kg 1m off the ground:

1kg = 10N so 30kg x 10N = 300 N

300N x 1m = 300 J 

If the weightlifter takes 0.5 seconds to lift this, then to calculate the his power:

P = E/t (W= J/s) so

P= 300J / 0.5s = 600 W

Kilowatt-hours (kWh)s are the units of energy supplied by mains electricity

Energy = Power x Time

      J  =  W x  s   > scaled up

 kWh = kW x h

Cost of electricty = Number of kWhs x cost per kWh

Cost effectiveness means value for money. There are three things to take into account when comparing this:

1) Buying + Installing costs                                2) Running costs     3) Environmental costs

As well as the payback time, efficiency and how effective it is at doing its job e.g. U Values