Power (Oxford AQA IGCSE Combined Science Double Award)
Revision Note
Power
Machines, such as car engines, transfer energy from one energy store to another constantly over a period of time
The rate of this energy transfer, or the rate of work done, is called power
Time is an important consideration when it comes to power
Two cars transfer the same amount of energy, or do the same amount of work to accelerate over a distance
If one car has more power, it will transfer that energy, or do that work, in a shorter amount of time
Cars with different power ratings
Power is defined as
Energy transferred per unit time
Therefore, power can be calculated using the equation
Where:
P = power in watts (W)
E = energy transferred in joules (J)
t = time in seconds (s)
Energy transferred is equivalent to work done
energy transferred = work done
Therefore, power can also be calculated using the equation
Where:
P = power in watts (W)
W = work done in joules (J)
t = time in seconds (s)
Worked Example
Calculate the energy transferred when an iron with a power rating of 2000 W is used for 5 minutes.
Answer:
Step 1: List the known values
Power, P = 2000 W
Time, t = 5 minutes = 5 × 60 = 300 s
Step 2: Write down the relevant equation
Step 3: Rearrange for energy transferred, ΔE
Step 4: Substitute in the known values
Examiner Tip
Since work done = force × distance, work done provides a mathematical link between forces and energy. This is commonly used in exam questions.
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