Energy and Efficiency

• Gravitational potential
• kinetic
• heat
• strain
• light
• nuclear
• chemical
• elastic potential
• electrical
• sound

We can change all energy from one type to another (IN--OUT)

Energy in=Energy out

E.G.120J=120J

Useful and wasted energy

useful and wasted energy is the energy that comes out.

Sankey Diagram

What is efficiency?

• How much useful energy you get out compared to energy put in

How to calculate efficiency

E.g. A light bulb gives out 50J of light, if 400J of electrical energy is put in calculate efficiency

Efficiency= 50/400 =0.125

%=12.5%

• All electrical appliances use electrical energy
• The power rating(w) tells us how much energy an appliance uses every second

e.g. 40w=40 joules per second

E=p x t

Energy transfer(J)=Power(w) x time(s)

E.G. a 1800w hairdryer is used for 10 minutes. Caluculate energy transfer,give the units.

E=p x t

1800 x 600 =1080000J

• The kilowatt hour is a unit electricity meters record the mains electrical energy transformed into units of kilowatt hour.One kilowatt hour is the energy transformed by kilowatt devices in 1 hour.

E.G. A 3 kilowatt electrical kettle is used 6 times for 5minutes each time.

3kw x 30/60=1.5