Lesson 4.2.3

4.2.3 Resistance Quiz: OCR Physics, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 4.2.3, Resistance: 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. Resistance is defined as:

    • R = I / V, measured in ohms
    • R = V / I^2, measured in ohms
    • R = V I, measured in ohms
    • R = V / I, measured in ohms

  2. According to Ohm's law at constant temperature, current is directly proportional to what?

    • Electric charge
    • Power
    • Potential difference
    • Resistance

  3. What happens to the resistance of a filament lamp as its temperature increases?

    • It stays zero
    • It decreases
    • It increases
    • It remains constant

  4. What happens to the resistance of an NTC thermistor when temperature increases?

    • It remains constant
    • It increases
    • It doubles
    • It decreases

  5. In which direction does an ideal semiconductor diode allow current to flow?

    • Both directions equally
    • Reverse direction only
    • Alternating direction only
    • Forward direction only

  6. What happens to the resistance of a light-dependent resistor as light intensity increases?

    • It remains constant
    • It becomes infinite
    • It decreases
    • It increases

  7. Under what condition does a light-emitting diode emit light?

    • Reverse bias
    • Infinite resistance
    • Forward bias
    • Zero potential difference

  8. A resistor passes 0.25 A when the potential difference across it is 6 V. What is its resistance?

    • 6.25 Ω
    • 24 Ω
    • 1.5 Ω
    • 0.04 Ω

  9. A resistor of 5 Ω carries a current of 3 A. What is the potential difference across it?

    • 8 V
    • 1.7 V
    • 15 V
    • 2 V

  10. On an I-V graph, a point gives 2 V and 0.04 A. What is the resistance at that point?

    • 0.08 Ω
    • 0.02 Ω
    • 50 Ω
    • 500 Ω

  11. A filament lamp has a resistance of 12 Ω at 6 V. At 12 V its current is 0.8 A. What is its resistance at 12 V?

    • 12 Ω
    • 9.6 Ω
    • 15 Ω
    • 24 Ω

  12. An LDR has resistance 2 kΩ in bright light and 200 kΩ in darkness. What is the ratio of its dark resistance to its bright resistance?

    • 1000
    • 10
    • 0.01
    • 100

  13. A diode carries 20 mA when the forward p.d. across it is 0.7 V. What is its resistance at this point?

    • 14 Ω
    • 0.0286 Ω
    • 70 Ω
    • 35 Ω

  14. The resistance of an NTC thermistor is 500 Ω at 20 C and 100 Ω at 60 C. By what percentage has its resistance fallen?

    • 80%
    • 20%
    • 5%
    • 400%

  15. What quantity is represented by the gradient of a current-voltage graph?

    • Resistance
    • Power
    • Reciprocal of resistance
    • Potential difference

  16. How is resistance determined at a specific point on a curved current-voltage graph?

    • V multiplied by I
    • V divided by I
    • Tangent gradient
    • Area under curve

  17. What happens to potential difference across a fixed resistor in series with an LDR as light intensity increases?

    • It decreases
    • It increases
    • It remains constant
    • It drops to zero

  18. What happens to the resistance of a diode as forward potential difference exceeds threshold voltage?

    • It stays zero
    • It remains constant
    • It decreases rapidly
    • It increases rapidly

  19. A 1.5 V cell in series with a resistor passes 0.6 A. What is the resistance of the resistor? Assume no internal resistance.

    • 2.5 Ω
    • 0.9 Ω
    • 0.4 Ω
    • 1.5 Ω

  20. An LED needs about 2 V across it. It is connected to a 5 V supply in series with a resistor, with 20 mA through the circuit. What resistance is needed?

    • 60 Ω
    • 250 Ω
    • 150 Ω
    • 100 Ω

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