AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), 2019: Question 1

💡 Key knowledge

• An ammeter measures current and must be connected in series.
• A voltmeter measures potential difference and must be connected in parallel across the component.
• For a fixed resistor at constant temperature, current and potential difference are directly proportional.
• Use the equation V = IR .

🧠 Exam technique

• Read the circuit carefully: series means the component is in the same loop.
• When asked for a relationship, use the exact wording the mark scheme wants: directly proportional.
• For calculations, always write the equation first, then substitute numbers, then rearrange.
• Include units in the final answer: Ω for resistance.

❌ Common errors

• Putting the ammeter in parallel — this is wrong.
• Putting the voltmeter in series — this is wrong.
• Saying current “slows down” instead of decreases; the mark scheme allows “decreased”.
• Saying “inversely proportional” for a resistor at constant temperature.

✅ Correct answer

Ammeter in series with the resistor; voltmeter in parallel with the resistor.

💡 Key knowledge

• The ammeter measures the current flowing through the resistor, so it must be part of the same loop.
• The voltmeter measures the potential difference across the resistor, so it must be connected across it.

🧠 Exam technique

In multiple choice tables, match both columns correctly. One correct pairing gains the mark only if the full row is right.

✅ Correct answer

The current decreased.

💡 Key knowledge

Increasing resistance makes it harder for charge to flow, so the current gets smaller.

❌ Common errors

Some students wrote “slows down”. The mark scheme says this is not needed; the marking point is that the current decreased.

✅ Correct answer

Reverse the connections to the cell.

💡 Key knowledge

• Negative readings happen when the direction of current is reversed relative to the meter connections.
• The mark scheme also accepts reverse the cell or reverse the battery.

🧠 Exam technique

If a question asks for negative values, think about reversing polarity rather than changing the meters.

✅ Correct answer

Directly proportional.

💡 Key knowledge

For an ohmic resistor at constant temperature, if potential difference increases, current increases by the same proportion.

❌ Common errors

• Do not say inversely proportional.
• Do not say indirectly proportional.
• For 1 mark, the exact phrase matters.

✅ Correct answer

potential difference = current × resistance

or V = IR

💡 Key knowledge

Potential difference can also be called voltage, and both mean the same thing in this context.

🧠 Exam technique

You can earn the mark with the word equation or the symbol equation. Make sure it is written correctly and clearly.

📐 Calculations — step by step

1. Write the equation: V = IR
2. Substitute the values: 3.0 = 0.12 × R
3. Rearrange: R = 3.0 ÷ 0.12
4. Calculate: R = 25
5. Include the unit: 25 Ω

✅ Correct answer

Resistance = 25 Ω

❌ Common errors

• Using the wrong equation, such as I = VR .
• Forgetting to rearrange before calculating.
• Missing the unit Ω .
• Writing the answer as 0.25 Ω or 250 Ω due to a calculator slip.

💡 Remember these facts

• Ammeter: series
• Voltmeter: parallel
• Resistance increased → current decreased
• Negative readings → reverse the cell
• Ohmic resistor: directly proportional
• V = IR

🧠 Best exam habit

When stuck, ask: “Is this about the circuit setup, the direction of current, the relationship, or the calculation?” That helps you choose the right GCSE physics idea quickly.