AQA GCSE Physics Physics Paper 1 (Higher), June 2022: Question 6

10 marks · Standard Demand difficulty · Short Answer

Explain the functions of step-up and step-down transformers in the National Grid and calculate the charge flow given energy transferred and potential difference.

Practise this question

Question

An exam question with three parts based on Figure 8, which diagrams electricity supply via the National Grid showing a power station, transformer X, overhead transmission cables, transformer Y, and consumers. Part 06.1 (4 marks) asks to explain why transformer X is used. Part 06.2 (2 marks) asks to explain why transformer Y is used. Part 06.3 (4 marks) provides data for a town in Australia supplied by a battery (energy transferred = 3.24 x 10^11 J, potential difference = 230 V) and asks to calculate the charge flow to 3 significant figures.
Question text

06 Figure 8 shows how electricity is supplied to consumers by the National Grid.

Figure 8

06.1 Explain why transformer X is used in the National Grid.

[4 marks]

06.2 Explain why transformer Y is used in the National Grid.

[2 marks]

06.3 The town of Hornsdale in Australia has electricity supplied by a huge battery.

On one day the battery transferred 3.24 × 1011 J of energy to the town.

The potential difference of the town’s electricity supply is 230 V.

Calculate the charge flow to the town on this day.

Use the Physics Equations Sheet.

Give your answer to 3 significant figures.

[4 marks]

Charge flow (3 significant figures) = C

Mark scheme

Show the mark scheme A mark scheme showing answers for questions 06.1, 06.2, and 06.3. For 06.1, marks are awarded for stating transformer X increases potential difference, decreases current, reduces thermal energy transfer, and increases efficiency. For 06.2, marks are awarded for stating transformer Y decreases potential difference to a safe value. For 06.3, the calculation steps are shown substituting energy and potential difference into the appropriate equation to yield 1.41 x 10^9 C.

AO /

Question Answers Extra information Mark

Spec. Ref.

06.1 transformer X increases 1 AO1

potential difference 4.2.4.3

and decreases current do not accept if student states 1

that potential difference

decreases

reducing (thermal) energy do not accept no energy transfer 1

transfer to surroundings to surroundings

or

reducing (thermal) energy

transfer from transmission

cables

increasing the efficiency (of 1

power transmission)

AO /

Spec. Ref.

06.2 transformer Y decreases the 1 AO1

potential difference 4.2.4.3

to a safe / safer value dependent on scoring 1st 1

marking point– HYSICS – –

AO /

Spec. Ref.

06.3 3.24 × 1011 = Q × 230 1 AO2

4.2.4.2

3.24×1011 1

Q =

Q = 1 408 695 652 (C) 1

Q = 1.41 × 109 (C) allow correct rounding of an 1

or incorrect answer using data

16 Q = 1 410 000 000 (C) from the question

– HYSICS – –

Total Question 6 10

Question 7

How to answer it

Study Guide: The National Grid & Charge Flow

What this question tests

This question assesses your understanding of how the National Grid operates, specifically the role of step-up and step-down transformers in minimizing energy loss during power transmission. It also tests your ability to apply the energy and charge flow equation ( E = Q × V ), rearrange formulas, substitute standard form numbers correctly, and round to a specified number of significant figures.

Question 06.1 [4 marks]

Explain why transformer X is used in the National Grid.

✅ Correct Answer Breakdown

  • Mark 1: Transformer X increases the potential difference (step-up transformer).
  • Mark 2: This causes a decrease in current through the transmission cables.
  • Mark 3: Reduced current reduces thermal energy transfer to the surroundings (or reduces energy loss in cables).
  • Mark 4: This increases the overall efficiency of power transmission.

💡 Key Knowledge

  • Transformer X is a step-up transformer located near the power station.
  • By increasing voltage, the current drops dramatically. Because thermal energy lost in cables depends on resistance and current squared ( P = I²R ), keeping current low saves massive amounts of energy.

🧠 Exam Technique & Examiner Insights

  • Examiners note that students often lose marks by saying potential difference "decreases" or claiming there is "no energy transfer." Be precise: voltage increases, current decreases, energy loss decreases.

❌ Common Errors

  • Saying that transformer X reduces voltage (confusing it with transformer Y).
  • Failing to link the drop in current directly to reduced thermal energy loss in the wires.
Question 06.2 [2 marks]

Explain why transformer Y is used in the National Grid.

✅ Correct Answer Breakdown

  • Mark 1: Transformer Y decreases the potential difference.
  • Mark 2: To a safe / safer value for domestic/consumer use.
Note: The second mark is strictly dependent on scoring the first marking point!

💡 Key Knowledge

  • Transformer Y is a step-down transformer located near towns and cities.
  • It reduces the high transmission voltage down to 230 V, which is safe for homes and businesses to use.

🧠 Exam Technique

  • Keep explanations concise for 2-mark questions. State what the transformer does to the voltage and why that makes it suitable for consumers.
Question 06.3 [4 marks]

Calculate the charge flow to the town on this day (3 sig figs).

📐 Step-by-Step Calculation

  1. State the formula: Energy transferred = Charge flow × Potential difference ( E = Q × V ) or ( Q = E / V ). [1 mark]
  2. Substitute values: 3.24 × 10¹¹ = Q × 230 [1 mark]
  3. Rearrange & Calculate: Q = (3.24 × 10¹¹) / 230 = 1 408 695 652 C [1 mark]
  4. Apply Significant Figures: 1.41 × 10⁹ C (or 1 410 000 000 C ) [1 mark]

🧠 Exam Technique & Formatting

  • Always write out the unrounded calculator answer first before rounding. This protects you against method/rounding errors.
  • Make sure your final answer clearly displays 3 significant figures as requested in the stem.

❌ Common Calculation Traps

  • Forgetting how to input standard form ( × 10¹¹ ) correctly into scientific calculators, leading to power-of-ten errors.
  • Rounding to 3 decimal places instead of 3 significant figures.

Topics

Physics · P2: Electricity · P7: Magnetism and Electromagnetism

Question and mark scheme from the AQA GCSE Physics examination, Physics Paper 1 (Higher), June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.