AS Level Physics chapter 10: D.C. circuits MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

78 exam-style questions on D.C. circuits, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

78 questions · 3 topics · 10 per test

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What chapter 10 covers

Ten D.C. circuits questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. A 12 V supply of negligible internal resistance drives current through two resistors in series, 20 Ω and 40 Ω. What is the current?

  1. A
    0.2 A
  2. B
    0.3 A
  3. C
    0.6 A
  4. D
    1.2 A
Show answer

Answer: A. Total R = 60 Ω; I = 12 ÷ 60 = 0.20 A.

2. In a circuit diagram, a component is drawn as a small rectangle with a single straight line running through it along its length, joining the wires at each end. What is the component?

  1. A
    a resistor
  2. B
    a fuse
  3. C
    a thermistor
  4. D
    a variable resistor
Show answer

Answer: B. The fuse symbol is a rectangle with a line through it lengthways. A plain rectangle is a resistor; a diagonal arrow makes it variable; a diagonal line with a short bent tail makes it a thermistor.

3. A potentiometer wire 1.00 m long has a p.d. of 2.0 V across its whole length. A cell of e.m.f. 1.2 V is connected for comparison. What is the balance length?

  1. A
    6.0 cm
  2. B
    40.0 cm
  3. C
    60.0 cm
  4. D
    167 cm
Show answer

Answer: C. The p.d. per unit length is 2.0 V per 100 cm, so balance length = 1.2/2.0 × 100 = 60.0 cm. 167 cm comes from inverting the ratio.

4. Electromotive force (e.m.f.) is defined as

  1. A
    the force on electrons in a wire
  2. B
    the energy transferred per unit charge in driving charge round a complete circuit
  3. C
    the p.d. across the external resistor
  4. D
    the current from a cell
Show answer

Answer: B. E.m.f. is energy converted (from chemical, for a cell) per unit charge, in joules per coulomb (volts).

5. In a potentiometer used to compare e.m.f.s, the galvanometer reads zero when the sliding contact is at the balance point. Why does this method measure e.m.f. accurately?

  1. A
    because the wire has zero resistance
  2. B
    because no current is drawn from the cell being tested, so there is no p.d. across its internal resistance
  3. C
    because the galvanometer has zero resistance
  4. D
    because the driver cell has no e.m.f.
Show answer

Answer: B. At balance no current flows through the test cell, so its terminal p.d. equals its e.m.f.

6. Which pair of facts is used to derive the formula 1/R = 1/R1 + 1/R2 for two resistors in parallel?

  1. A
    the p.d. across each resistor is the same, and the currents in the resistors add up to the total current
  2. B
    the current is the same in each resistor, and the p.d.s add up to the supply p.d.
  3. C
    the p.d. across each resistor is the same, and the current in each resistor is the same
  4. D
    the currents add up to the total current, and the p.d.s add up to the supply p.d.
Show answer

Answer: A. Same V across each (second law round each loop) and I = I1 + I2 (first law) give V/R = V/R1 + V/R2; dividing by V gives the formula.

7. A fixed 4.0 kΩ resistor is in series with a variable resistor that can be set anywhere from 0 to 12 kΩ, across an 8.0 V supply of negligible internal resistance. The output is taken across the variable resistor. What is the range of the output p.d.?

  1. A
    0 to 6.0 V
  2. B
    0 to 8.0 V
  3. C
    2.0 V to 6.0 V
  4. D
    2.0 V to 8.0 V
Show answer

Answer: A. At 0 Ω the output is 0 V; at 12 kΩ it is 8.0 × 12/16 = 6.0 V. The output can never reach the full 8.0 V while the fixed resistor takes a share.

8. A large protective resistor is connected in series with the galvanometer at the start of a potentiometer experiment and is short-circuited once the balance point is nearly found. Why?

  1. A
    it protects the galvanometer from large currents far from balance, and removing it makes the galvanometer more sensitive near balance
  2. B
    it raises the p.d. across the wire so that balance can be reached
  3. C
    it reduces the internal resistance of the test cell
  4. D
    it makes the balance length longer and so reduces the percentage uncertainty
Show answer

Answer: A. Far from balance the current through the galvanometer could be large. Near balance the resistor is removed so that even a tiny imbalance gives a visible deflection, and the null point can be found precisely.

9. Points X and Y are joined by two branches. Branch 1 is a cell of e.m.f. 6.0 V in series with a 2.0 Ω resistor; branch 2 is a cell of e.m.f. 3.0 V in series with a 1.0 Ω resistor. Both cells have negligible internal resistance and both have their positive terminals connected to X. What is the p.d. between X and Y?

  1. A
    3.0 V
  2. B
    4.0 V
  3. C
    4.5 V
  4. D
    6.0 V
Show answer

Answer: B. The cells oppose each other round the loop: I = (6.0 − 3.0) ÷ (2.0 + 1.0) = 1.0 A. Then VXY = 6.0 − 1.0 × 2.0 = 4.0 V, which checks with 3.0 + 1.0 × 1.0 = 4.0 V.

10. Which of these quantities is a potential difference rather than an electromotive force?

  1. A
    the energy per unit charge transferred from light to electrical energy by a solar cell
  2. B
    the energy per unit charge transferred from kinetic to electrical energy by a dynamo
  3. C
    the energy per unit charge transferred from chemical to electrical energy by a battery
  4. D
    the energy per unit charge transferred from electrical to thermal energy in a resistor
Show answer

Answer: D. E.m.f. describes energy transferred into electrical energy (at a source); p.d. describes electrical energy transferred into other forms (in a component). Only the resistor converts electrical energy into another form.

Start the chapter testAbout the AS Level Physics test

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Ways to practise this chapter

D.C. circuits: questions students ask

How many D.C. circuits MCQs are there?

78, each with the answer and a short explanation, across 3 topics: Practical circuits, Kirchhoff’s laws, Potential dividers. Every chapter test draws ten of them, so you can take it many times.

Is the AS Level Physics chapter 10 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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