AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), 2023: Question 2

✅ Correct answer

Draw the voltmeter symbol V and connect it across the two resistors (in parallel with the resistor pair).

Mark idea: 1 mark for the voltmeter symbol correctly placed across the resistors.

💡 Key knowledge

• A voltmeter measures potential difference.
• It must be connected in parallel with the component(s) you want to measure.
• Here, the question asks for the p.d. across the two resistors together.

🧠 Exam technique

• Place the voltmeter across the whole resistor section, not in the main loop.
• Make sure the circuit symbol is clear and recognisable.

❌ Common errors

• Putting the voltmeter in series.
• Connecting it across just one resistor when the question wants both.
• Drawing an ammeter symbol instead of a voltmeter.

✅ Correct answer

The total resistance must be less than 20 Ω because the two resistors are connected in parallel, and the total resistance of resistors in parallel is less than the resistance of the smallest resistor.

Two separate marking points: one for “less than 20 Ω”, one for the parallel-resistance explanation.

💡 Key knowledge

• For resistors in parallel, the total resistance is always smaller than the smallest branch resistance.
• So if one resistor is 20 Ω, the combined resistance must be below 20 Ω.

🧠 Exam technique

• Use the word parallel explicitly.
• If you can, compare to the smallest resistor: that earns the reasoning mark.

❌ Common errors

• Saying the total resistance is more than 20 Ω.
• Just writing “because the resistors are in parallel” without explaining what that means.
• Confusing this with series, where resistances add.

✅ Correct answer

potential difference = current × resistance

or V = IR

1 mark for the correct equation.

💡 Key knowledge

• V = potential difference in volts (V)
• I = current in amperes (A)
• R = resistance in ohms (Ω)

🧠 Exam technique

If you forget symbols, write the full words: potential difference = current × resistance. That is fully acceptable.

❌ Common errors

• Writing V = I ÷ R.
• Mixing up current and resistance.
• Using the wrong units.

📐 Calculations

1. Convert current from mA to A: 480 mA = 0.48 A
2. Use V = IR
3. Substitute values: V = 0.48 × 7.5
4. Calculate: V = 3.6 V

Final answer: 3.6 V

✅ Correct answer

3.6 V

Marking points were awarded for converting 480 mA to 0.48 A, substituting into the equation, and giving the correct final value.

🧠 Exam technique

• Always convert mA to A before calculating.
• Check your answer has the correct unit: V.
• Use a sensible number of significant figures: here 3.6 V matches the data.

❌ Common errors

• Using 480 instead of 0.48.
• Forgetting the unit conversion from mA to A.
• Giving the answer in Ω instead of V.

✅ Correct answer

Label the axes:

• x-axis: resistance of R in Ω
• y-axis: total resistance (of resistors) in Ω

Plot the two missing points from Table 1 correctly and draw a curved line of best fit.

💡 Key knowledge

• Graph axes must include quantity + unit.
• For these results, the relationship is not a straight line, so a curve is needed.
• The plotted points from the table are:
  (5, 4.0), (10, 6.7), (15, 8.6), (20, 10.0), (25, 11.1)

🧠 Exam technique

• Plot points carefully, aiming within ½ small square.
• Draw a smooth curve through the trend, not point-to-point straight lines.
• If there were an outlier, ignore it only if the question allows it; here all table values should be used.

❌ Common errors

• Forgetting to label axes.
• Swapping x and y axes.
• Plotting the wrong coordinates.
• Drawing a straight line when the data clearly curves.

✅ Correct answer

A resistance of about 14 Ω gives a total resistance of 4.4 Ω.

The mark scheme accepts a value consistent with the line of best fit, within ½ small square.

💡 Key knowledge

• Read across from 4.4 Ω on the y-axis to the curve, then down to the x-axis.
• This is an estimate, not an exact table value.

🧠 Exam technique

• Use a ruler to read the graph carefully.
• Answer with a value that fits the curve, not necessarily a neat whole number.

❌ Common errors

• Reading from the wrong axis.
• Ignoring the line of best fit and using the nearest plotted point instead.
• Giving a value far from the curve.

✅ Correct answer

The difference between the two values is due to a random error.

1 mark for “random”.

💡 Key knowledge

• A random error causes measurements to vary without a fixed pattern.
• Small changes in how a person stands on the scales can change the reading slightly.

🧠 Exam technique

If the question asks for the type of error, use the exact term: random error.

❌ Common errors

• Saying systematic error.
• Writing just “error” without naming it.
• Describing the equipment instead of the type of error.

✅ Correct answer

From the graph, category A has a body water percentage of about 61%, and category B has about 68%.

The student’s body water percentage is 64.1%, which is between 45% and 65%, so:

• if the student is in category A, they have a healthy body water percentage
• if the student is in category B, they have an unhealthy body water percentage

Therefore, the student could be in category A or category B, but the health judgement is different for each category.

💡 Key knowledge

• Read values from the graph carefully.
• Use the given healthy range: 45% to 65%.
• Then compare the student’s value of 64.1% to that range.

🧠 Exam technique

• Top-level answers use evidence from the graph plus the health range.
• Say what happens for both categories because the student could fit either one.
• State a clear conclusion rather than leaving the answer as a list of numbers.

❌ Common errors

• Not using the graph values for category A and B.
• Forgetting the healthy range is 45%–65%.
• Saying the student is definitely healthy without checking category B.
• Not explaining that category A is healthy but category B is not.

💡 Remember

• Voltmeter goes in parallel.
• Parallel resistance is less than the smallest resistor.
• V = IR is essential for calculations.
• Convert mA to A before calculating.
• Graphs need correct labels, points, and line of best fit.
• Use the word random for an unpredictable measurement difference.

🧠 How marks were earned

• Short factual answers were enough for the 1-mark recall questions.
• Explanations gained marks when they included the physics reason, not just the answer.
• Calculation marks came from correct method, conversion, and final unit.
• Graph questions needed accuracy and a sensible curve, not a rushed straight line.