Physics - 1 Conservation and Dissipation of Energy - 1.8 Electrical Appliances & 1.9 Energy and Power

Light bulb

- useful: light emitted from glowing filament
- wasted: energy transfer from filament heating surroundings

Electric heater

- useful: energy heating surroundings
- wasted: light from glowing filament

Electric toaster

- useful: energy heating bread
- wasted: energy heating toaster case and surroundings

Electric kettle

- useful: energy heating water
- wasted: energy heating kettle and surroundings

Hairdryer

- useful: kinetic energy of air from fan, energy heating air from filament
- wasted: sound of fan motor, energy heating hairdryer

Electric motor

- useful: kinetic energy of object driven by motor, GPE of objects lifted
- wasted: energy heating motor, sound waves from motor

How does a clockwork radio function?

a spring is wound inside, increasing its elastic potential energy. This energy is transferred to its KE store as it turns an electric generator.

Power is...

the rate at which energy is transferred

The more powerful an appliance...

the faster it transfers energy

Power is measured in:

Watts, W

1 Watt =

1 J/s

Equation for power:

power = energy transferred OR work done ÷ time taken for transfer

Symbol equation for power:

P = E OR W ÷ t