1. Efficiency Efficiency = Useful energy output X 100% Energy Input Energy Input

2. Efficiency  Efficiency is the comparison between the amount of useful energy produced (output energy) and the original amount of energy used (input energy).

3. Efficiency  Efficiency is often expressed as a percentage. The percent efficiency is simply the efficiency multiplied by 100%

4. Efficiency  Some devices are much more efficient than others.  For example, an electric motor typically has a percent efficiency of over 80%, whereas an incandescent light bulb has a percent efficiency for producing light energy of only 5%.

5. Sample Calculations  Determine the percent efficiency of a 60-W fluorescent light bulb that uses 2000 J of electrical energy to produce 400 J of light energy.  DATA EQUATION

6. Improving Efficiency  In Canada it is now required by federal law that special “Energuide” information be attached to each appliance.  This label states the amount of electrical energy per year the appliance uses.  Consumers can compare the Energuid number for all the refrigerators of the same capacity and make an informed decision about which one is the most efficient model.

7. Sample Questions  1. Calculate the percent efficiency of an electric motor that uses 15 000 J of energy to produce 11 500 J of useful energy.  2. Calculate the percent efficiency of an incandescent light bulb that produces 2500 J of light energy from 50 000 J of electrical energy.