types of energy
- Gravitational potential
- elastic potential
We can change all energy from one type to another (IN--OUT)
conservative of energy
Energy in=Energy out
Useful and wasted energy
useful and wasted energy is the energy that comes out.
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
Energy and power
- 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