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Power (Oxford AQA IGCSE Combined Science Double Award)

Revision Note

Leander Oates
Oxford AQA Combined Science Double Award: PhysicsOxford AQA Physics

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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    Leander Oates

    Author: Leander Oates

    Expertise: Physics

    Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.

    Caroline Carroll

    Author: Caroline Carroll

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    Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about creating high-quality resources to help students achieve their full potential.