AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), June 2025: Question 3

12 marks · Standard Demand difficulty · Short Answer

Investigate the resistance of a resistor by drawing a circuit diagram, calculating resistance from ammeter and voltmeter readings, sketching an I-V graph, and determining suitable resistors based on power ratings.

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Question text

03 A student investigated the resistance of a resistor.

03.1 The student used:

• the resistor

• a cell

• a switch

• an ammeter

• a voltmeter.

Draw a circuit diagram for a circuit the student could use to measure the resistance of

the resistor. 10

[3 marks]

The student:

• added a variable resistor to the circuit

• used the variable resistor to change the readings on the ammeter and the voltmeter

• recorded several different pairs of readings from the ammeter and the voltmeter.

03.2 When the reading on the ammeter was 450 mA, the reading on the voltmeter

was 2.7 V.

Calculate the resistance of the resistor.

Use the Physics Equations Sheet.

[4 marks]

11 Resistance = Ω

03.3 The student plotted a graph of current against potential difference for the

fixed resistor.

Complete Figure 2 to show a sketch graph for a fixed resistor at a

constant temperature.

[1 mark]

Figure 2

03.4 Figure 3 shows five resistors with the same resistance but different power ratings.

Figure 3

The power rating of a resistor is the maximum energy the resistor can transfer each

second without overheating.

Each resistor has a resistance of 2.2 kΩ.

*11*Determine which resistors in Figure 3 are suitable to be used in a circuit that has a

maximum current of 0.012 A.

Use the Physics Equations Sheet.

[4 marks]

Suitable resistors

Mark scheme

Show the mark scheme

Question 3

AO /

Question Answers Extra information Mark

Spec. Ref.

03.1 circuit with a cell, (switch) and allow battery for cell 1 AO2

resistor in series

ammeter in series (with the 1 AO1

resistor and the cell)

voltmeter in parallel with resistor 1 AO1

6.2.1.1

AO /

Spec. Ref.

03.2 I = 0.45 (A) subsequent marks may be 1 AO2

awarded if an incorrectly / not 6.2.1.3

converted value of I is used

2.7 = 0.45 × R 1

2.7 1

R =

0.45

R = 6 (Ω) allow 6.0 (Ω) 1

AO /

Spec. Ref.

03.3 straight line through the origin in 1 AO1

both 1st and 3rd quadrant– – 8464/P/1H – 6.2.1.4

AO /

Spec. Ref.

03.4 R = 2200 (Ω) subsequent marks may be 1 AO2

awarded if an incorrectly / not

converted value of R is used

P = 0.0122 × 2200 1 AO2

P = 0.3168 (W) allow P = 0.32 1 AO2

allow P = 0.317

resistors A, B and C dependent on MP1 and MP3 1 AO3

the first three marks may be 6.2.4.1

12 awarded for calculating Imax for

any of the resistors

R = 2200 (Ω) (1) subsequent marks may be

awarded if an incorrectly / not

converted value of R is used

2.0 = I2 × 2200 (1)

I = 0.030…(1)

resistors A, B and C (1) dependent on MP1 and MP3

Total Question 3 12

How to answer it

AQA GCSE Physics: Resistance, Characteristics & Power Ratings

📋 What this question tests

This question evaluates your core practical and theoretical understanding of electrical circuits:

Circuit drawing: Correct standard circuit symbols, series loops, and placing voltmeters in parallel.
Ohm's Law calculations: Applying V = I × R with metric milli-unit conversions ( mA → A ).
I-V characteristics: Identifying the current-voltage graph for an ohmic conductor across positive and negative voltages.
Electrical power: Calculating power using P = I² × R , converting kΩ → Ω , and evaluating real-world component limits.

Question 03.1 • 3 Marks

Drawing the Resistance Measurement Circuit

Circuit design using correct symbols

✅ Mark Scheme Requirements

1 Mark Circuit contains a cell (or battery), a switch, and the resistor all connected in a series loop.
1 Mark Ammeter connected in series with the cell and resistor.
1 Mark Voltmeter connected in parallel across the resistor only.

What to draw: A single continuous rectangular loop containing: a cell (long thin line + short thick line), an open or closed switch symbol, a circle with an 'A' (ammeter), and a plain rectangle (fixed resistor). Connect two branch wires from either side of the fixed resistor to a circle with a 'V' (voltmeter) in parallel.

🧠 Exam Technique & Common Pitfalls

Symbol precision: A resistor is a clean, plain rectangle. Do not draw a line through it (that is a fuse) or an arrow through it (that is a variable resistor).
Meter placement: Remember: Ammeter goes Around the main loop (series); Voltmeter makes a V-shaped detour around the component (parallel).
Gaps: Ensure circuit wires cleanly join components without stray gaps or crossing lines.

Question 03.2 • 4 Marks

Calculating Resistance from Current and Potential Difference

Applying Ohm's Law with unit conversions

📐 Step-by-Step Calculation

1 Convert mA to A:
Current must be in amperes:
I = 450 mA ÷ 1000 = 0.45 A 1 Mark

2 Substitute into equation:
Using V = I × R :
2.7 = 0.45 × R 1 Mark

3 Rearrange for R:
R = 2.7 ÷ 0.45 1 Mark

4 Calculate final answer:
R = 6 Ω (or 6.0 Ω ) 1 Mark

❌ Common Errors & Examiner Commentary

Forgetting to convert units: Calculating 2.7 ÷ 450 = 0.006 Ω loses the unit conversion mark and usually penalises the final answer mark.
Inverting the division: Calculating 0.45 ÷ 2.7 instead of 2.7 ÷ 0.45 . Always write down the base equation first to avoid rearranging mistakes.
Carried-forward marks: Even if you fail to convert mA to A, you can still gain marks for substitution and rearrangement if carried through correctly.

Question 03.3 • 1 Mark

Current–Potential Difference Graph for a Fixed Resistor

I-V characteristics of an Ohmic Conductor

✅ Correct Answer

A single straight line that passes directly through the origin (0,0), extending continuously into both the 1st quadrant and the 3rd quadrant.

Visual Check: Place your ruler across the origin. Draw a constant positive slope line running from the bottom-left quadrant (negative V, negative I) straight through the center (0,0) to the top-right quadrant (positive V, positive I).

💡 Key Knowledge

A fixed resistor at a constant temperature is an ohmic conductor.
Current is directly proportional to potential difference ( I ∝ V ).
Because resistance remains constant in both directions, the line must be completely straight and symmetrical across both positive and negative axes.
Exam trap: Stopping at the origin (0,0) only gives half the graph and scores 0 marks.

Question 03.4 • 4 Marks

Selecting Resistors by Safe Power Rating

Calculating power dissipation and component selection

📐 Step-by-Step Method

1 Convert resistance unit (kΩ to Ω):
R = 2.2 kΩ = 2.2 × 1000 = 2200 Ω 1 Mark

2 Substitute into Power equation:
Using P = I² × R (from Physics Equations Sheet):
P = (0.012)² × 2200 1 Mark

3 Calculate power dissipated:
P = 0.000144 × 2200 = 0.3168 W (allow 0.32 W) 1 Mark

4 Determine suitable resistors:
A resistor is safe if its rating is greater than or equal to the power dissipated (0.3168 W):
• A (2.0 W) > 0.3168 W (Safe)
• B (1.0 W) > 0.3168 W (Safe)
• C (0.5 W) > 0.3168 W (Safe)
• D (0.25 W) < 0.3168 W (Will overheat!)
• E (0.125 W) < 0.3168 W (Will overheat!)
Suitable resistors: A, B and C 1 Mark

❌ Common Errors & Misconceptions

Forgetting to square the current: Calculating P = I × R = 0.012 × 2200 = 26.4 W . Remember the formula is P = I²R !
Misunderstanding power rating: The rating is the maximum safe limit. A resistor will overheat and fail if the circuit power exceeds its rating. Therefore, choose resistors rated higher than 0.3168 W.
Selecting only C: While C is the closest safe value, the question asks which resistors are suitable, so all three that can handle the power (A, B, and C) must be listed.

Topics

Physics · P2: Electricity

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 1 (Higher), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.