Efficiency (Edexcel GCSE Physics: Combined Science)
Revision Note
Author
LeanderExpertise
Physics
Efficiency
- The efficiency of a system is a measure of the amount of wasted energy in an energy transfer
- Efficiency is defined as:
The ratio of the useful energy output from a system to its total energy output
- If a system has high efficiency, this means most of the energy transferred is useful
- If a system has low efficiency, this means most of the energy transferred is wasted
- Efficiency can be represented as a decimal or as a percentage
- The equation for efficiency is:
Worked example
The blades of a fan are turned by an electric motor. In one second, 300 J of energy is transferred electrically from the mains supply to the fan. 85 J is wasted due to friction and sound.
Calculate the percentage efficiency of the motor.
Step 1: List the known quantities
-
- Total energy supplied to the device (input) = 300 J
- Total wasted energy = 85 J
Step 2: State the equation
Step 3: Determine total energy transferred by the device (output)
-
- Due to the conservation of energy:
-
- Therefore, total energy transferred by the device (output) = 300 J
Step 4: Calculate the useful energy transferred by the device (output)
-
- Due to conservation of energy
Step 5: Substitute these values into the efficiency equation
Exam Tip
Efficiency can be in a ratio (between 0 and 1) or percentage format (between 0 and 100%)If the question asks for efficiency as a ratio, give your answer as a fraction or decimal.
If the answer is required as a percentage, remember to multiply the ratio by 100 to convert it:
- if the ratio = 0.25, percentage = 0.25 × 100 = 25 %
Remember that efficiency has no units (only %)
You've read 0 of your 0 free revision notes
Get unlimited access
to absolutely everything:
- Downloadable PDFs
- Unlimited Revision Notes
- Topic Questions
- Past Papers
- Model Answers
- Videos (Maths and Science)
Did this page help you?