AQA AS Level Physics Paper 2, June 2022: Question 33

1 mark · Easy difficulty · Multiple Choice

Identify that the relationship between currents at a junction (I1 + I2 + I3 + I4 = 0) is an expression of the law of conservation of charge.

Practise this question

Question

Multiple choice question showing a junction of four wires with currents I1, I2, I3, and I4 meeting at a central point, where the relationship I1 + I2 + I3 + I4 = 0 is given. Four options are provided: A charge., B energy., C potential difference., D power., with answer boxes next to each.
Question text

33 The currents in the four wires obey the relationship I1 + I2 + I3 + I4 = 0

This relationship is an expression of the law of conservation of

[1 mark]

A charge.

B energy.

C potential difference.

D power.

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer is A (charge.).

33 A (AO1) charge.

How to answer it

Conservation of Charge in Electric Circuits

What this question tests

This question assesses your fundamental understanding of Kirchhoff's First Law and its underlying physical principle: the conservation of charge at an electrical junction. You need to link algebraic equations representing currents meeting at a node directly to fundamental conservation laws.

Question 3.3 [1 Mark]

Exam Breakdown

✅ Correct Answer

A (charge)

Mark awarded: 1 mark for selecting option A (AO1 - Knowledge and Understanding).

💡 Key Knowledge

  • Kirchhoff's First Law: The sum of the currents entering any junction in a circuit is equal to the sum of the currents leaving that junction ( ΣI = 0 if sign conventions are used).
  • Electric Current Definition: Current is the rate of flow of charge ( I = ΔQ / Δt ).
  • Because charge cannot be created or destroyed at a point in a circuit, the total charge arriving at a junction per unit time must equal the total charge leaving it per unit time.

🧠 Exam Technique

For multiple-choice questions testing definitions or fundamental laws (AO1), make sure you immediately link physical quantities to their conservation principles:

  • Current relates to charge.
  • Potential difference (p.d.) relates to energy (specifically work done per unit charge).

❌ Common Errors

  • Confusing Kirchhoff's First Law (conservation of charge, current-based) with Kirchhoff's Second Law (conservation of energy, potential difference-based).
  • Guessing option B (energy) because energy conservation is the most commonly memorised conservation law in mechanics. Always read the physical quantity involved in the equation ( I for current) first.

Topics

Physics · 3.5 Electricity

Question and mark scheme from the AQA AS Level Physics examination, Paper 2, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.