Lesson 4.2.5

4.2.5 Power Quiz: OCR Physics, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 4.2.5, Power: 20 multiple choice questions for the OCR Physics (H156), Unit 3: Electrons, waves and photons, written with Revision Ninja.

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The 20 questions

  1. Which pair of expressions gives the electrical power dissipated in a resistor of resistance R carrying current I, with potential difference V across it?

    • P = IR^2 and P = V^2 R
    • P = I^2 R and P = V^2/R
    • P = I^2/R and P = VR
    • P = IR and P = V/R

  2. The unit of electrical power is:

    • joule (J)
    • watt (W)
    • volt (V)
    • kilowatt-hour (kW h)

  3. The kilowatt-hour (kW h) is a unit of:

    • charge
    • energy
    • potential difference
    • power

  4. How many joules are there in 1 kW h?

    • 3.6 x 10^3 J
    • 1.0 x 10^3 J
    • 3.6 x 10^6 J
    • 6.0 x 10^4 J

  5. Which combination of units is equivalent to the joule?

    • V A s
    • V A / s
    • A / (V s)
    • V / (A s)

  6. A lamp rated at 60 W operates from a 230 V supply. What current does it draw?

    • 0.0038 A
    • 13800 A
    • 0.26 A
    • 3.8 A

  7. A 10 ohm resistor carries a current of 2.0 A. What power is dissipated in it?

    • 20 W
    • 5.0 W
    • 80 W
    • 40 W

  8. A 4.0 ohm resistor has 12 V across it. What power does it dissipate?

    • 48 W
    • 9.0 W
    • 3.0 W
    • 36 W

  9. A 2.0 kW heater runs for 3.0 hours. How much energy does it transfer, in kW h?

    • 2.0 kW h
    • 6.0 kW h
    • 0.67 kW h
    • 3.0 kW h

  10. A 2.0 kW heater runs for 3.0 hours at 15 p per kW h. What is the cost?

    • 6 p
    • 45 p
    • 90 p
    • GBP 9.00

  11. A 100 W bulb operates for 5.0 minutes. How much energy is transferred, in joules?

    • 3.0 x 10^2 J
    • 3.0 x 10^4 J
    • 5.0 x 10^2 J
    • 1.8 x 10^6 J

  12. A 6.0 V cell delivers a current of 0.50 A to an external circuit. What is the power output of the cell?

    • 12 W
    • 3.0 W
    • 6.5 W
    • 0.083 W

  13. Which circuit arrangement of two identical resistors dissipates more total power from a fixed voltage?

    • both dissipate equal
    • series
    • neither dissipates power
    • parallel

  14. A heater of resistance R dissipates power P from a fixed supply. It is replaced by one of resistance R/2 on the same supply. What is its new power?

    • 2P
    • P/2
    • 4P
    • P

  15. The current through a fixed resistor doubles. By what factor does the power dissipated in it change?

    • half
    • 4 times
    • unchanged
    • 2 times

  16. A 12 V supply drives a current through a 6.0 ohm resistor in series with a 2.0 ohm resistor. What power is dissipated in the 6.0 ohm resistor?

    • 27 W
    • 13.5 W
    • 9.0 W
    • 18 W

  17. A 2.2 kW kettle on a 230 V supply heats 1.5 kg of water from 20 C to 100 C (c = 4200 J/kg/K). Assuming 100% efficiency, how long does it take?

    • 38 s
    • 229 s
    • 1100 s
    • 504 s

  18. A motor takes 500 W of electrical power and delivers 350 W of useful mechanical output. What is its efficiency?

    • 30%
    • 350%
    • 143%
    • 70%

  19. A 60 W lamp runs at 230 V for 2.0 hours. How much energy does it transfer, in kW h?

    • 1.2 kW h
    • 30 kW h
    • 0.06 kW h
    • 0.12 kW h

  20. What is the main advantage of transmitting electricity at high voltage?

    • reduced wire resistance
    • increased transformer output
    • increased current speed
    • reduced current losses

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