2. Energy transformations in circuits
What happens to the electrical energy received by a lamp in a circuit?
5 J transformed into light energy
electrical energy from battery 100 J
95 J transformed into heat energy
Most of the energy from the battery does not produce light – most of it is wasted as heat!

3. Calculating energy efficiency
The efficiency of an energy transfer can be calculated using this formula:
total energy input
useful energy output
% efficiency =
× 100
This bulb converts 200 J of electrical energy from the circuit into 10 J of useful light energy: 10
% efficiency =
× 100
200 = 5%

4. Energy efficiency activity

5. Energy efficiency summary

6. Why should electricity usage be reduced?
Most of our electricity is generated by burning fossil fuels in power stations.
These emit massive amounts of carbon dioxide into the air which causes global warming.
We also have to pay for the electricity we use. If we can spend less money on electricity, then we have more to spend on the things we enjoy.
Photo credit: © 2011 Jupiterimages Corporation

7. Reducing our electricity bills
There are several ways that you can help to reduce the amount of electricity you use every day.
Using electrical appliances less. This is the most effective way to reduce the amount of energy you use – think about whether the electricity that you’re using is necessary.
Photo credit: © 2011 Jupiterimages Corporation
Making sure devices are turned off. Simply leaving electrical equipment, such as televisions, on stand-by can waste energy.

8. Reducing our electricity bills
There are several ways to make your house more energy efficient.
Energy efficient light bulbs These bulbs are more efficient than normal light bulbs.
Insulation This minimizes the amount of heat lost from a house, meaning that less energy is needed to keep it warm.
Photo credit (lightbulb): stock.xchng
Photo credit (insulation): © 2011 Jupiterimages Corporation
Some modern houses have been designed to reduce the amount of energy they use. 8