Electrical Power (AQA GCSE Physics): Revision Notes
2.3.1 Electrical Power
Power
Power is the rate at which energy is transferred. Because work done is the transfer of energy, power also tells us the rate at which work is done.
The unit of power is the Watt (W).
- It is directly proportional to current and voltage.
- Power loss is proportional to resistance and to the square of the current.
Formula
- Power, , measured in watts, W
- Energy transferred, , measured in Joules, J
- Time, , measured in seconds, s
Example: Question: Marianne switches on a toaster for 50 seconds. During this time, the toaster uses 700J of electricity. Calculate the power of the toaster.
1. Write out the appropriate equation.
For this question, the correct equation is:
2. Substitute in the numbers.
We know the values for energy and time taken, so we can simply substitute them in.
Example:
2. Work Done
Where:
- power, , in watts, W
- time,, in seconds, s
- work done, , in joules, J
Question: What is the power of a car engine that does 4500J of work in 1.5 minutes?
1. Write out the appropriate equation.
In this situation, the appropriate equation is:
2. Work out the value for time.
In the question, we have been given a value for time in minutes. The equation requires us to give the time in seconds, so we need to convert.
3. Substitute in the numbers.
Now that we have the correct values, we can put the numbers into our equation.