Lesson 3.5.1.2

3.5.1.2 Current-voltage characteristics Quiz: AQA Physics, Unit 5

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.5.1.2, Current-voltage characteristics: 20 multiple choice questions for the AQA Physics (7408), Unit 5: Electricity, written with Revision Ninja.

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The 20 questions

  1. Ohm's law states that:

    • current is proportional to potential difference at constant physical conditions
    • current is proportional to the square of potential difference
    • potential difference is proportional to resistance at all currents
    • resistance varies with current for an ohmic conductor

  2. The I-V graph of an ohmic conductor is:

    • a curve through the origin with decreasing gradient
    • a straight line through the origin
    • a curve that rises steeply after a threshold
    • a straight line with a non-zero intercept

  3. A silicon semiconductor diode in forward bias conducts appreciably only above a threshold of about:

    • 100 V, the reverse breakdown voltage
    • the supply frequency in volts
    • zero volts at all forward voltages
    • 0.6 to 0.7 V

  4. As the current through a filament lamp increases, its resistance:

    • decreases to zero at high current
    • increases, because the filament heats and lattice vibrations impede electrons
    • decreases, because the filament cools
    • stays constant because the lamp is ohmic

  5. An ideal voltmeter has:

    • variable resistance that depends on the reading
    • infinite resistance
    • a resistance equal to the circuit's resistance
    • zero resistance

  6. An ideal ammeter has:

    • zero resistance
    • a resistance equal to that of the component it measures
    • a resistance of 1 ohm
    • infinite resistance

  7. On a V-I graph with V on the vertical axis, the gradient of an ohmic conductor's line equals:

    • the charge per unit time
    • its conductance
    • its resistance
    • the power dissipated

  8. Which component has a constant ratio of V to I at every point on its characteristic?

    • the filament lamp
    • the semiconductor diode
    • all three components
    • the ohmic conductor

  9. A filament lamp carries 0.20 A when the potential difference across it is 6.0 V. What power does it dissipate?

    • 30 W
    • 6.2 W
    • 1.2 W
    • 0.033 W

  10. A silicon diode is reverse biased with a small reverse voltage. What current flows approximately?

    • a current proportional to the reverse voltage
    • a large current that flows immediately
    • the same current as in forward bias
    • a very small current, close to zero, until breakdown

  11. A resistor has I = 0.15 A at V = 3.0 V. What is the current at V = 6.0 V if it is ohmic?

    • 0.30 A
    • 0.075 A
    • 0.45 A
    • 0.60 A

  12. A filament lamp carries 0.10 A at 2.0 V and 0.15 A at 4.0 V. What is its resistance at 4.0 V?

    • about 27 ohm
    • about 40 ohm
    • about 20 ohm
    • about 15 ohm

  13. A diode carries 20 mA at a forward voltage of 0.70 V. What is its resistance at this point?

    • 14 ohm
    • 35 ohm
    • 350 ohm
    • 0.029 ohm

  14. On a filament lamp's V-I graph (V on the vertical axis), the gradient at high voltage compared with low voltage is:

    • the same, so the resistance is constant
    • larger, so the resistance is higher at high voltage
    • zero at high voltage
    • smaller, so the resistance is lower at high voltage

  15. A student says a filament lamp obeys Ohm's law because its resistance is steady. Which evaluation is best?

    • No, a filament lamp's resistance rises as it heats, so its I-V graph curves and it is not ohmic.
    • Yes, resistance falls as the filament heats up.
    • No, the lamp has zero resistance at low voltage.
    • Yes, the lamp's I-V graph is a straight line through the origin.

  16. A lamp has 3.0 V giving 0.20 A, and 6.0 V giving 0.30 A. By roughly how much does its resistance change?

    • about 0.75 times as great at 6.0 V
    • 1.5 times greater at 6.0 V
    • about 1.3 times greater at 6.0 V
    • two times greater at 6.0 V

  17. A 6.0 V supply is connected in series with a 100 ohm resistor and a silicon diode with 0.70 V forward voltage. What current flows?

    • 53 mA
    • 60 mA
    • 86 mA
    • 6 mA

  18. A lamp's resistance is 5 ohm at 6 V and 6 ohm at 12 V. Which explanation is best?

    • The filament heats more at 12 V, raising its resistance, so the lamp is non-ohmic.
    • The filament cools at 12 V, so its resistance falls.
    • Ohm's law holds, so the resistance should be the same at both voltages.
    • The lamp's resistance depends only on the supply frequency.

  19. An ideal voltmeter is connected in parallel with a 100 ohm resistor in a circuit. What current flows through the voltmeter?

    • half the circuit current
    • the full circuit current, since it is in parallel
    • a current equal to V/100
    • zero, since its resistance is infinite

  20. A 9.0 V supply has a 200 ohm series resistor and a silicon diode with 0.65 V forward voltage. What current flows?

    • 45 mA
    • 9 mA
    • 70 mA
    • 42 mA

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