AQA GCSE Physics Physics Paper 1 (Higher), June 2023: Question 1

✅ Correct Answer

• Transformer X causes the potential difference to increase. [1 mark]
• Transformer X causes the current to decrease. [1 mark]

Note: Answers must be in this exact order.

💡 Key Knowledge

Transformer X is situated between the power station and transmission cables, meaning it is a step-up transformer:

• Increases potential difference (voltage) to very high levels (e.g. 400 kV).
• Decreases the current in the transmission cables.
• Lower current means significantly less thermal energy is wasted as heat in the cables ( P = I²R ).

🧠 Exam Technique

Always identify the position of the transformer first:

• Near power station: Step-up (Voltage goes UP, current goes DOWN).
• Near consumers/homes: Step-down (Voltage goes DOWN, current goes UP to safe, usable levels).

❌ Common Errors

• Swapping the words around (writing "decrease" then "increase").
• Writing "step up" or "higher" instead of complete verbs like "increase" or "rise".

✅ Correct Box to Tick

P = I² R

Ticking the 3rd box scores [1 mark]. All other options are incorrect.

💡 Physics Equations Sheet Check

The question reminds you to use the Physics Equations Sheet. Even if you have memorised it, double-check:

• P = I² R relates power ( P ), current ( I ), and resistance ( R ).
• P = VI is power, potential difference, and current.
• V = IR is Ohm's Law (potential difference, current, resistance).

🧠 Exam Technique

Always write out your substitution before rearranging. If you make a slip on your calculator, the examiner can still award 1 mark for substitution and 1 mark for rearrangement.

❌ Common Errors

• Forgetting to square the current: Dividing 1.60 × 10⁹ by 2000 instead of 2000² (gives 800,000 Ω — completely incorrect!).
• Bracket mistakes on calculators: Typing 1.60 × 10⁹ / 2000² without brackets can sometimes lead to order-of-operation errors depending on the calculator model.

✅ Correct Answer

efficiency = useful energy output / total energy input

Also accepted: useful output energy transfer / total input energy transfer

[1 mark]

🧠 Top Tip

Remember that efficiency is always a fraction or percentage where output is compared to input:

Useful OUT / Total IN

Since efficiency cannot exceed 1 (or 100%), the smaller number (useful output) is always on top!

💡 Unit Watch: GJ (Gigajoules)

Notice the question already has GJ on the answer line and gives the input in GJ. You do not need to convert to joules ( × 10⁹ ). Keeping it in GJ saves time and prevents standard form errors!

❌ Common Errors

• Dividing instead of multiplying: Calculating 34.2 / 0.992 = 34.48 GJ . This gives an output larger than the input, which is physically impossible (efficiency cannot exceed 100%).
• Multiplying by 100: The efficiency is already given as a decimal ( 0.992 ), not a percentage ( 99.2% ). Multiplying by 100 here leads to an answer 100 times too big.