AQA AS Level Physics Paper 2, June 2025: Question 18

1 mark · Easy difficulty · Multiple Choice

Identify which component from the given data is an ohmic conductor with the smallest resistance.

Practise this question

Question

A table showing potential difference V from 0.0 V to 10.0 V in 2.0 V steps alongside current I for components A, B, C, and D. Component A has current increasing by 0.3 A per 2.0 V step. Component B has current increasing non-linearly from 0.0 to 3.3 A. Component C has current increasing by 0.6 A per 2.0 V step. Component D has current increasing non-linearly from 0.0 to 3.2 A. The question asks which component is the ohmic conductor that has the smallest resistance.

Mark scheme

Show the mark scheme Mark scheme table row indicating for question 18 the correct response is C, assessed under AO2.

How to answer it

Identifying Ohmic Conductors and Comparing Resistance

📋 What this question tests

This question assesses your understanding of Ohm's Law (direct proportionality between current and potential difference) and your ability to calculate and compare electrical resistance (R = V / I) using tabular data.

Question 18 Analysis

Multiple Choice (1 Mark)

✅ Correct Answer: C

Component C is the only ohmic conductor with the smaller resistance.

  • Ohmic: The ratio V / I remains constant at 3.33 Ω for all values.
  • Smallest Resistance: Compared to Component A ( 6.67 Ω ), Component C allows double the current for the same voltage, meaning its resistance is lower.

💡 Key Knowledge

  • Ohm's Law: Current I through a conductor is directly proportional to potential difference V across it, provided physical conditions (like temperature) remain constant.
  • Tabular Test for Linearity: Equal increases in V must result in equal increases in I (i.e. ΔI / ΔV = constant ).
  • Resistance Formula: R = V / I . A higher gradient on an I–V graph indicates a lower resistance.

📐 Step-by-Step Component Evaluation

  1. Step 1: Check for Ohmic Behaviour (Constant Ratio / Linear Rate)
    Component Current at 2.0 V Current at 10.0 V Current change per 2.0 V (ΔI) Is it Ohmic?
    A 0.3 A 1.5 A Constant: +0.3 A each step Yes
    B 1.5 A 3.3 A Decreasing: +1.5, +0.8, +0.4, +0.4, +0.2 No (Filament lamp type)
    C 0.6 A 3.0 A Constant: +0.6 A each step Yes
    D 0.0 A 3.2 A Increasing: 0.0, +0.2, +1.0, +1.0, +1.0 No (Diode / non-linear)
  2. Step 2: Calculate and Compare Resistance for the Ohmic Conductors (A and C)

    Calculate R = V / I at any non-zero point (e.g. V = 10.0 V ):

    • Component A: R = 10.0 V / 1.5 A = 6.67 Ω
    • Component C: R = 10.0 V / 3.0 A = 3.33 Ω
  3. Step 3: Select the Ohmic Conductor with the Smallest Resistance

    3.33 Ω < 6.67 Ω , so Component C has the smaller resistance.

🧠 Exam Technique & Speed Tip

You do not need to calculate R for every value to answer this quickly in Paper 1:

  • Check column intervals first: notice ΔI = 0.3 A for A and 0.6 A for C are constant, instantly eliminating B and D.
  • For a given voltage (e.g. 10.0 V), a larger current means a smaller resistance because R ∝ 1/I . Since C has 3.0 A vs A's 1.5 A , C has half the resistance.

❌ Common Errors

  • Choosing B: Component B draws the highest initial current ( 1.5 A at 2.0 V), leading students to pick it for "lowest resistance" while forgetting it must be ohmic.
  • Confusing current and resistance: Mistaking the component with the largest resistance for the one with the smallest resistance (picking A instead of C).
  • Reciprocal confusion: Forgetting that on an I–V characteristic, the gradient is 1/R , not R . A steeper slope represents a lower resistance.
Mark Scheme Reference: 18 = C (AO2 — Application of knowledge in an electrical circuit context). Award 1 mark for option C.

Topics

Physics · 3.5 Electricity

Question and mark scheme from the AQA AS Level Physics examination, Paper 2, June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.