AQA A-Level Physics Paper 1, June 2023: Question 27

1 mark · Medium difficulty · Multiple Choice

Identify which box of resistors and wires gives the same reading on both ammeters when connected into the given circuit.

Practise this question

Question

A circuit diagram showing a cell and two ammeters connected to a four-terminal box where the top left terminal is X. Four alternative configurations of internal wiring labeled A, B, C, and D are shown below, each containing different arrangements of identical resistors and connecting wires.
Question text

27 A box with four terminals is connected to a cell and two ammeters. The top left terminal

is X.

Each of the boxes A to D is connected into the circuit in turn. All the resistors have equal

resistance.

Which box gives the same reading on both ammeters?

[1 mark]

A B

C D

A

B

C

D

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer is option D.

27 D

How to answer it

Analyzing Ammeter Readings in Black Box Circuits

What this question tests

This question assesses your understanding of electric circuits, Kirchhoff's First Law (conservation of charge), and how current behaves in series versus parallel arrangements. You must analyze the path of current through a two-port network connected to two separate ammeters.

Question Part 27

Identifying the correct box for equal ammeter readings

✅ Correct Answer

Box D

Mark Allocation: 1 mark

💡 Key Knowledge

  • The left ammeter is in the main loop connected directly in series with the cell. It measures the total current leaving the power source.
  • The right ammeter is connected across the right-hand terminals.
  • For both ammeters to show the same reading, the exact same total current flowing through the left ammeter must also pass completely through the right ammeter without splitting or bypassing.

🧠 Exam Technique

Trace the current path methodically from terminal X :

  • In Box D, current enters top-left ( X ), passes horizontally through the single top resistor to the top-right terminal, goes through the right ammeter, and loops back via the bottom wire connection (which is just a direct conducting path with no branching resistors).
  • Because there are no parallel branches or alternative routes to divert charge, 100% of the current measured by the first ammeter goes straight through the second ammeter.

❌ Common Errors

  • Choosing boxes containing multiple resistors (like A, B, or C) which introduce parallel junctions or voltage dividers, causing the current to split and leading to differing ammeter values.
  • Confusing series current conservation with potential difference rules.

Topics

Physics · 3.5 Electricity

Question and mark scheme from the AQA A-Level Physics examination, Paper 1, June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.