Lesson 4.2.4

4.2.4 Resistivity Quiz: OCR Physics, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 4.2.4, Resistivity: 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 equation defines the resistivity rho of a material in terms of resistance R, length L and cross-sectional area A?

    • rho = RA/L
    • rho = RL/A
    • rho = A/(RL)
    • rho = L/(RA)

  2. What is the SI unit of resistivity?

    • ohm
    • ohm per metre
    • ohm metre
    • ohm metre squared

  3. For a uniform wire, electrical resistance is directly proportional to which quantity?

    • length
    • diameter
    • resistivity
    • cross-sectional area

  4. Which factor affects the resistivity of a metallic conductor?

    • shape
    • cross-sectional area
    • length
    • temperature

  5. A metal wire has resistance 2.0 ohm. Its length is doubled and its cross-sectional area is halved, with temperature constant. What is the new resistance?

    • 16 ohm
    • 8.0 ohm
    • 1.0 ohm
    • 4.0 ohm

  6. In a resistivity experiment, what dimension is measured using a micrometer?

    • wire diameter
    • wire mass
    • cross-sectional area
    • wire length

  7. As the temperature of a metal increases, its resistivity:

    • stays exactly constant
    • decreases
    • falls to zero
    • increases

  8. As the temperature of a semiconductor increases, its resistivity usually:

    • becomes infinite
    • decreases
    • increases linearly
    • stays the same

  9. The resistance of an NTC thermistor as its temperature rises:

    • decreases
    • becomes infinite
    • stays constant
    • increases

  10. What does NTC stand for in the context of a thermistor?

    • Nominal thermal capacity
    • Normal temperature current
    • Non-thermal conductor
    • Negative temperature coefficient

  11. Why does the resistivity of a metal increase as temperature rises?

    • increased lattice vibrations
    • decreased electron collisions
    • increased charge density
    • reduced drift velocity

  12. A wire of length 2.0 m and cross-sectional area 0.50 mm^2 has resistance 0.40 ohm. What is its resistivity?

    • 4.0 x 10^-7 ohm m
    • 2.5 x 10^-8 ohm m
    • 1.0 x 10^-7 ohm m
    • 1.0 x 10^-6 ohm m

  13. A copper wire is 10 m long with diameter 0.40 mm and resistivity 1.7 x 10^-8 ohm m. What is its resistance?

    • 0.14 ohm
    • 1.35 ohm
    • 2.7 ohm
    • 13.5 ohm

  14. A wire of resistivity 4.0 x 10^-7 ohm m and length 4.0 m has resistance 5.0 ohm. What is its cross-sectional area?

    • 1.25 x 10^-7 m^2
    • 3.2 x 10^-8 m^2
    • 3.2 x 10^-7 m^2
    • 8.0 x 10^-7 m^2

  15. Why must the current be kept small when determining the resistivity of a wire?

    • prevent temperature rise
    • prevent wire melting
    • prevent magnetic effects
    • prevent insulation breakdown

  16. A graph of resistance R against length L for a wire of constant cross-sectional area is a straight line through the origin. Its gradient equals:

    • rho x A
    • 1/(rho A)
    • A/rho
    • rho/A

  17. A uniform rod of resistivity rho is stretched so that its length doubles while its volume stays constant. Its new resistance is how many times the original?

    • 2 times
    • 8 times
    • half
    • 4 times

  18. Two wires of the same material and length have diameters in the ratio 2:1. What is the ratio of resistance of the thick wire to the thin wire?

    • 1:8
    • 4:1
    • 1:4
    • 1:2

  19. Which two dimensions of a wire are needed alongside its resistance to calculate resistivity?

    • diameter and density
    • length and diameter
    • volume and length
    • length and mass

  20. How does resistance change for an NTC thermistor when heated?

    • it increases
    • it becomes zero
    • it remains constant
    • it decreases

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