AQA GCSE Physics Physics Paper 1 (Higher), November 2021: Question 3

10 marks · Standard Demand difficulty · Extended Answer

Describe an experimental method to investigate the current-potential difference characteristics of a resistor, explain the effect of temperature on the results, and compare analogue and digital ammeters.

Practise this question

Question

The question presents a circuit diagram in Figure 2 showing a series circuit with a DC power supply, a switch, an ammeter, a fixed resistor R with a voltmeter connected across it in parallel, and a variable resistor. Part 03.1 asks for a 6-mark method to investigate how current varies with potential difference for both positive and negative values. Part 03.2 asks how an increase in temperature would affect the results (2 marks). Figure 3 shows a moving-coil ammeter scale spanning 0 to 2.0 A with marks at 0.2 A intervals and a needle pointing near 1.34 A. Part 03.3 asks for the resolution of this ammeter. Figure 4 shows a digital ammeter reading 1.34 A, and part 03.4 asks for one other reason why using the digital ammeter is better.
Question text

03 Student A investigated how the current in resistor R at constant temperature varied

with the potential difference across the resistor.

Student A recorded both positive and negative values of current.

Figure 2 shows the circuit Student A used.

Figure 2

03.1 Describe a method that Student A could use for this investigation.

[6 marks]

03.2 Student B repeated the investigation.

During Student B’s investigation the temperature of resistor R increased.

Explain how the increased temperature of resistor R would have affected

Student B’s results.

[2 marks]

Figure 3 shows the scale on a moving coil ammeter at one time in the investigation.

Figure 3

03.3 What is the resolution of the moving coil ammeter?

[1 mark]

13 Resolution = A

*0113.*4 Student B replaced the moving coil ammeter with a digital ammeter.

Figure 4 shows the reading on the digital ammeter.

Figure 4

The digital ammeter has a higher resolution than the moving coil ammeter.

Give one other reason why it would have been better to use the digital ammeter

throughout this investigation.

[1 mark]

Mark scheme

Show the mark scheme Mark scheme for Question 3 outlining marks totaling 10. For 03.1, a level-of-response grid awards up to 6 marks for an experimental procedure that includes varying the variable resistor, measuring current and potential difference, reversing power supply connections, switching off between readings to prevent heating, and plotting an I-V graph. For 03.2, 2 marks are awarded for stating that current and p.d. would not be directly proportional (or graph would be curved) because the resistance of resistor R increases. For 03.3, 1 mark is given for 0.2 (A). For 03.4, 1 mark is given for less chance of misreading, no parallax error, or giving a reading closer to the true value.

Question 3

AO/

Question Answers Mark

Spec. Ref

03.1 Level 3: The method would lead to the production of a valid AO1

5–6

outcome. All key steps are identified and logically sequenced. 4.2.1.4

RPA4

Level 2: The method would not necessarily lead to a valid

outcome. Most steps are identified, but the plan is not fully logically 3–4

sequenced.

Level 1: The method would not lead to a valid outcome. Some

1–2

relevant steps are identified, but links are not made clear.

No relevant content 0

Indicative content

• measure the current in R using the ammeter

• measure the p.d. across R using the voltmeter

• vary the resistance of the variable resistor

(or vary the number of cells or use a variable power supply)

• record a range of values of current and p.d.

• ensure current is low to avoid temperature increase

• switch circuit off between readings

• reverse connection of R to power supply

• repeat measurements of I and V in negative direction

• plot a graph of current against p.d.

AO /

Question Answers Extra information Mark

Spec. Ref.

03.2 current and p.d. would not be 1 AO3

directly proportional 4.2.1.4

or RPA4

I-V graph would not be straight

or

I-V graph would be curved

(because) resistance of R would 1

increase

03.3 0.2 (A) 1 AO3

4.2.2

RPA4

any one from:

03.4 1 AO3

• less chance of misreading 4.2.2

• no parallax error allow position of eye(s) does not

RPA4

affect reading

• it can give a reading closer to allow ‘it is more accurate’

the true value

ignore ‘no human error’

ignore ‘easier to read’

Total 10

How to answer it

Required Practical: Investigating Current-Voltage Characteristics

What this question tests

This question focuses on AQA Required Practical 4 (RPA 4): determining the current-voltage characteristics of a resistor at constant temperature.

  • Planning a valid investigation (6 marks): circuit setup, independent and dependent variables, controlling temperature, and obtaining negative values.
  • Scientific reasoning: explaining how resistance changes with temperature and how this curves an I-V graph.
  • Apparatus & measurements: reading analog meter scales (resolution) and evaluating the advantages of digital meters over analog moving-coil meters.
Question 03.1 • 6 Marks

Method: Determining Current vs Potential Difference for a Resistor

Describe a method that Student A could use for this investigation. Include how to obtain both positive and negative values.

✅ Model Answer (Level 3: 5–6 Marks)

  1. Initial readings: Turn on the switch. Read and record the current on the ammeter and the potential difference (p.d.) on the voltmeter.
  2. Vary the circuit: Adjust the variable resistor to change the resistance (or adjust the power supply) to obtain at least 5 different pairs of current and p.d. values.
  3. Maintain constant temperature: Switch off the circuit between readings (or keep current low) to prevent resistor R from heating up.
  4. Obtain negative values: Reverse the connections to the battery/power supply. Repeat the measurements to collect a range of negative current and p.d. values.
  5. Analysis: Plot a graph of current on the y-axis against potential difference on the x-axis.

🧠 Exam Technique & Mark Breakdown

This is a level of response question graded in 3 tiers:

  • Level 3 (5–6 marks): Fully coherent, logical method that leads directly to a valid outcome. Must mention reversing the battery/leads to get negative values and controlling temperature.
  • Level 2 (3–4 marks): Most steps present, but lacks detail on obtaining negative values or keeping temperature constant.
  • Level 1 (1–2 marks): Fragmented steps without clear sequencing (e.g. just says "measure current and voltage").

❌ Common Errors

  • Forgetting negative values: The prompt explicitly states Student A recorded negative values. Omitting "reverse the power supply / battery connections" caps your response at Level 2.
  • Ignoring temperature control: Failing to state "switch off between readings" means the resistor heats up, so it is no longer at constant temperature.
  • Confusing meter placement: Saying ammeter is in parallel or voltmeter in series. (Ammeter in series, voltmeter across R in parallel).

💡 Key Knowledge

  • Ohm's Law: Current is directly proportional to potential difference if temperature remains constant ( V = I × R ).
  • I-V Graph for an Ohmic Conductor: A straight line passing directly through the origin (0, 0), extending into the third quadrant (negative current and negative voltage).
Question 03.2 • 2 Marks

Effect of Temperature Rise on Results

Explain how the increased temperature of resistor R would have affected Student B's results.

✅ Mark Scheme Answer

Effect: The current and p.d. would no longer be directly proportional (or the I-V graph would be curved / not a straight line) [1 mark].

Reason: Because the resistance of resistor R would increase as temperature increases [1 mark].

💡 Microscopic Explanation

When the temperature of a metal resistor increases:

  • Metal lattice ions gain thermal energy and vibrate more vigorously with greater amplitude.
  • This increases the rate of collisions between conduction electrons and lattice ions.
  • More collisions = greater resistance.
Examiner Insight: Many students correctly state that resistance increases, but fail to explicitly state the consequence for the results (e.g. stating the graph curves or becomes non-linear). Make sure you answer both "what happens to the results" and "why".
Question 03.3 • 1 Mark

Reading Scale: Resolution of Moving Coil Ammeter

What is the resolution of the moving coil ammeter?

📐 Step-by-Step Resolution Calculation

  1. Identify major markings: The scale marks run from 0 to 1.0 A, and 1.0 A to 2.0 A.
  2. Count subdivisions: Between 0 and 1.0 A, there are exactly 5 equal spaces (intervals).
  3. Calculate value of 1 interval:
    Resolution = 1.0 A ÷ 5 = 0.2 A

✅ Answer

0.2 A

Only the number 0.2 is needed as "A" is already printed on the answer line.

❌ Common Trap

Counting tick marks instead of the spaces between them. Counting lines can mistakenly give 4 or 6 intervals, leading to incorrect values like 0.25 A or 0.1 A.

Question 03.4 • 1 Mark

Comparing Measuring Instruments: Digital vs Analog

The digital ammeter has a higher resolution. Give one other reason why it would have been better to use the digital ammeter throughout this investigation.

✅ Accepted Answers (Any ONE)

  • Less chance of misreading the scale.
  • No parallax error (or reading does not depend on viewing angle / eye position).
  • It gives a reading closer to the true value / is more accurate.

❌ Rejected Answers (Examiner Pitfalls)

  • "No human error" — Too vague! Humans can still misread or miscopy numbers from a digital screen.
  • "Easier to read" — Not scientific enough; must explain why (e.g. less chance of misreading or eliminates parallax error).
  • "More precise" — Precision is linked to resolution, which was already given in the question stem and excluded from credit.

Topics

Physics · Required Practicals · P2: Electricity · Required Practicals

Question and mark scheme from the AQA GCSE Physics examination, Physics Paper 1 (Higher), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.