1. Problem Solving Energy = the ability to do work Work = force (F) x distance (d) Force is measured in newtons (N) When a newton of force is applied for one metre of distance (1N.m), 1 joule of work is done. Power is the rate at which work is done. If a machine uses 1 watt of power, it uses 1 joule of energy in 1 second. 1W = 1J/s Power = energy/time

2. Problem: An aquarium light bulb uses 7 J of electric energy in one second. How many watts of power does this light bulb consume in 3s? Step 1 – Write down what you know. Step 2 – What do you want to find out? Step 3 – Use the formula Step 4 – Express the power in watts.

3. Problem: Speakers on a computer use 40 J of electric energy in one second. How many watts of power do the speakers consume in 60 s? Step 1 – Write down what you know. Step 2 – What do you want to find out? Step 3 – Use the formula Step 4 – Express the power in watts.

4. Problem: How much electric energy does a 240 W fan use if it is left on for two hours? Step 1 – Write down what you know. Step 2 – What do you want to find out? Step 3 – Use the formula Step 4 – Express the power in watts.

5. Problem: How much electric energy does a 255 W colour television use if it is on for 4 hours? Step 1 – Write down what you know. Step 2 – What do you want to find out? Step 3 – Use the formula Step 4 – Divide by 1000 to change W.h to kW.h Step 5 – Summarize your results:

6. Efficient Appliance – A term used to describe how completely the input energy is converted to accomplish the desired output energy. (An appliance that Wastes less energy is considered to be more efficient). Percent efficiency of an electric device = useful energy output x 100 total electric energy input

7. Problem: An electric motor has 100 J of electric energy supplied to it every Second. It produces 70 J of kinetic energy every second when it is Providing power to a water pump. What is the efficiency of the motor? Step 1 – Write down what you know. Step 2 – What do you want to find out? Step 3 – Use the formula Step 4 – Summarize your answer

8. Photosynthesis: Carbon dioxide + water + energy  glucose + oxygen Respiration: Glucose + oxygen  carbon dioxide + water + energy