Lesson 3.13

3.13 Electronics: semiconductors, signals and operational amplifiers Quiz: AQA Physics, Unit 13

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.13, Electronics: semiconductors, signals and operational amplifiers: 20 multiple choice questions for the AQA Physics (7408), Unit 13: Electronics (A-level option), written with Revision Ninja.

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The 20 questions

  1. What is the threshold voltage Vth of an enhancement-mode MOSFET?

    • the drain-source voltage when the device is switched off
    • the gate-source voltage above which a conducting channel forms between drain and source
    • the breakdown voltage of the gate oxide layer
    • the maximum current the drain can carry

  2. Why does a MOSFET gate have a very high input resistance?

    • the gate is connected directly to the drain
    • the gate is a diode in forward bias
    • the gate is a metal wire that carries a heavy current
    • the gate is insulated by an oxide layer, so almost no current flows into it

  3. How is a Zener diode used as a constant voltage reference?

    • it is used only as a light detector
    • it stores charge like a capacitor
    • it is run in reverse breakdown, where its voltage stays nearly constant over a range of currents
    • it is run in forward bias, conducting above about 0.7 V

  4. How is a photodiode used as a detector in photoconductive mode?

    • it is reverse biased, and its current is proportional to the light intensity
    • it generates current only at night
    • it is forward biased, and it produces a voltage in the dark
    • it emits light when it is illuminated

  5. How does a Hall effect sensor help to measure rotation in a tachometer?

    • it converts light into a voltage through a rotating disc
    • it generates heat in proportion to the current through it
    • it produces a voltage related to the magnetic field, which changes as a magnet passes it
    • it measures temperature from changes in resistance

  6. In analogue-to-digital conversion, what sets the number of voltage levels that can be represented?

    • the mass of the audio source
    • the sampling duration only
    • the number of bits per sample
    • the colour of the signal

  7. What must the sampling rate of a signal be, at minimum, to represent a signal of highest frequency f_max without loss?

    • at least half the highest frequency present
    • at least twice the highest frequency present
    • independent of the frequency of the signal
    • equal to the number of bits per sample

  8. How many voltage levels can an 8-bit analogue-to-digital converter represent?

    • 256
    • 128
    • 512
    • 8

  9. What is the denary value of the binary number 1010?

    • 10
    • 5
    • 12
    • 8

  10. A coil of inductance 10 mH is connected in parallel with a capacitor of capacitance 100 microfarad. What is the resonant frequency?

    • about 50 Hz
    • about 1.6 kHz
    • about 5.0 Hz
    • about 160 Hz

  11. A resonant filter has a centre frequency of 1.0 kHz and a bandwidth of 50 Hz. What is its Q factor?

    • 50
    • 1000
    • 20
    • 0.05

  12. A resonant filter with Q = 10 has a centre frequency of 500 Hz. What is its bandwidth?

    • 50 Hz
    • 500 Hz
    • 10 Hz
    • 5 Hz

  13. An ideal inverting amplifier has Rf = 10 k ohm and Rin = 1 k ohm. What is the voltage gain?

    • -10
    • +10
    • -0.1
    • -11

  14. A non-inverting amplifier has Rf = 9 k ohm and Rl = 1 k ohm. What is its voltage gain?

    • -10
    • 9
    • 10
    • 1

  15. A summing amplifier has feedback resistor Rf equal to each input resistor. Inputs are 1 V and 2 V. What is the output voltage?

    • -2.0 V
    • +3.0 V
    • -1.5 V
    • -3.0 V

  16. A difference amplifier has Rf / Rl = 5, with V+ = 2.0 V and V- = 1.5 V. What is the output?

    • 10 V
    • 2.5 V
    • 0.5 V
    • -2.5 V

  17. An ideal op-amp is used as a comparator. What is the output when V+ is greater than V-?

    • it is driven to the negative supply rail
    • it is driven to the positive supply rail
    • it is driven to zero volts
    • it sits at half the supply voltage

  18. Why does an ideal op-amp draw no current at its inputs?

    • its output current is infinite
    • its power supply supplies all of its input current
    • its input resistance is zero, so all the current flows in
    • its input resistance is infinite, so no current flows into either input

  19. Why is the inverting input of an inverting amplifier at 0 V, a virtual earth?

    • the very large open-loop gain forces the inverting input to the same potential as the grounded non-inverting input
    • the input resistor carries the full output voltage
    • the inverting input is connected to earth through a diode
    • the output is always zero, so the input is grounded

  20. Which is a limitation of a real operational amplifier?

    • infinite input impedance and zero output impedance at all frequencies
    • finite open-loop gain, with the gain falling off at high frequency
    • no need for a power supply
    • unlimited output current from the supply

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