1. 02/12/2018
Energy

2. The ULTIMATE energy source
02/12/2018
The sun is the ultimate source of all our energy.
For example, we often get energy from beef:
BEEF comes from COWS,
COWS eat GRASS,
GRASS gets energy from the sun by PHOTOSYNTHESIS

3. Gravitational potential
The 9 types of energy
02/12/2018
Type
3 example sources
Type
3 example sources
Heat
Kinetic (movement)
Nuclear
Sound
Light
Chemical
Electrical
Gravitational potential
Elastic potential

4. Electricity Light + heat
Energy changes
02/12/2018
To describe an energy change for a light bulb we need to do 3 steps:
1) Write down the starting energy:
3) Write down what energy types are given out:
2) Draw an arrow
Electricity Light + heat
What are the energy changes for the following…?
An electric fire
A rock about to drop
An arrow about to be fired

5. Conservation of Energy
02/12/2018
In any energy change there is ALWAYS some “waste” energy:
e.g. a light bulb:
Electricity Light heat
In this example HEAT is wasted – it’s given to the surroundings. Waste energy is virtually always heat and it’s always given to the surroundings.

6. Energy Transfer diagrams
02/12/2018
Consider a light bulb. Let’s say that the bulb runs on 100 watts (100 joules per second) and transfers 20 joules per second into light and the rest into heat. Draw this as a diagram:
“Input” energy
“Output” energy
20 J/s light energy
100 J/s electrical energy
80 J/s heat energy (given to the surroundings)

7. Example questions Consider a computer: Consider a kettle:
02/12/2018
Consider a computer:
150 J/s electrical energy
10 J/s wasted sound
20 J/s wasted heat
Useful light and sound
How much energy is converted into useful energy?
What is the computer’s efficiency?
Consider a kettle:
Work out each energy value.
What is the kettle’s efficiency?
Sound energy
Wasted heat
Heat to water
2000 J/s electrical energy

8. Efficiency
02/12/2018
Efficiency is a measure of how much USEFUL energy you get out of an object from the energy you put INTO it.
Efficiency = Useful energy given out by the device
Energy put into it
e.g. if 2000 joules of electrical energy are put into a kettle and 500 joules of heat energy are gained from it, its efficiency is 500/2000 x 100% = 25%
x100%

9. Some examples of efficiency…
02/12/2018
5000J of electrical energy are put into a motor. The motor converts this into 100J of movement energy. How efficient is it?
A laptop can convert 400J of electrical energy into 240J of light and sound. What is its efficiency? Where does the rest of the energy go?
A steam engine is 50% efficient. If it delivers 20,000J of movement energy how much chemical energy was put into it?