Revision NotesExam QuestionsPast Papers
GCSEPhysics: Combined ScienceOCR GatewayExam Questions7. Energy7.2 Power & Efficiency

Power & Efficiency (OCR Gateway GCSE Physics: Combined Science)

Exam Questions

47 mins13 questions

Select a question set to download for
7.2 Power & Efficiency

Select an answer set to view for
7.2 Power & Efficiency

Easy
Medium
11 mark

A motor has an input energy of 800 J. The useful output energy is 500 J.

What is the wasted energy?

  • 300 J

  • 500 J

  • 800 J

  • 1300 J

Choose your answer

Did this page help you?

11 mark

A gas fire, used to heat a room, has an input energy transfer of 180 000 J per minute.

The fire has an efficiency of 0.8.

Use the equation: Efficiency = Useful output energy transfer / Input energy transfer

Calculate the useful output energy transfer per minute.

  • 600 J

  • 2400 J

  • 36 000 J

  • 144 000 J

Choose your answer

Did this page help you?

2
Sme Calculator1 mark

A boiler has an input energy of 720 kJ from the gas it burns.

It transfers 540 kJ of useful energy to the home.

What is the efficiency of the boiler?

Use the equation: efficiency = useful output energy transfer ÷ total input energy transfer

  • 0.12

  • 0.75

  • 0.90

  • 1.33

Choose your answer

Did this page help you?

31 mark

A boiler has an input power of 12 kW from the gas it burns.

Its efficiency is 0.75.

Which row in the table shows the correct values for this boiler?

  Useful output power (kW) Wasted output power (kW)
A 3 9
B 8 4
C 9 6
D 9 3

    Choose your answer

    Did this page help you?

    41 mark

    A vehicle has an input power from fuel of 20 kW and a useful output power of 6 kW.

    Calculate the power it wastes.

    • 3 kW

    • 6 kW

    • 14 kW

    • 20 kW

    Choose your answer

    Did this page help you?

    51 mark

    A radio transfers 30 J of potential energy to 27 J of useful energy.

    What is the efficiency and energy loss for the radio?

      efficiency energy loss
    A 10% 3 J
    B 10% 27 J
    C 90% 3 J
    D 90% 27 J

      Choose your answer

      Did this page help you?

      61 mark

      Higher Only

       

      Which row would result in an increase in the efficiency of a machine?

       

      Increase the energy losses due to friction

      		 Increase the work output without
      changing the work input
      A Yes Yes
      B Yes No
      C No No
      D No Yes

        Choose your answer

        Did this page help you?

        71 mark

        Which wall would allow the most heat transfer through the wall?

        • A thick wall made from a material with high thermalconductivity.

        • A thick wall made from a material with low thermal conductivity.

        • A thin wall made from a material with high thermal conductivity.

        • A thin wall made from a material with low thermal conductivity.

        Choose your answer

        Did this page help you?