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 in cars, for IGCSE & GCSE Physics revision notes
Two cars accelerate to the same final speed, but the one with the most power will reach that speed sooner
  • Power is defined as

Energy transferred per unit time

  • Therefore, power can be calculated using the equation

P space equals fraction numerator space E over denominator t end fraction

  • 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

P space equals fraction numerator space W over denominator t end fraction

  • 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 

P space equals space E over t

Step 3: Rearrange for energy transferred, ΔE

E space equals space P space cross times space t

Step 4: Substitute in the known values

E space equals space 2000 space cross times space 300

E space equals space 600 space 000 space straight J

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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