AQA GCSE Combined Science: Trilogy Physics Paper 1 (Higher), 2020: Question 1

💡 Key knowledge

• In a UK plug: brown = live, blue = neutral, green/yellow = earth.
• UK mains supply is 230 V and 50 Hz.
• Neutral and earth are at the same potential, so the potential difference between them is 0 V.
• The earth wire is a safety wire. It provides a low-resistance path for current.

🧠 Exam technique

• Use the exact wire colours and terminal names in part (a).
• When asked for a value, write the number and unit clearly.
• For explanations, give two linked points for 2 marks.
• If drawing a symbol, make it neat and recognisable.

❌ Common errors

• Mixing up live and neutral.
• Forgetting the unit Hz or writing volts for frequency.
• Saying the person gets “power” instead of current through the body.
• Not mentioning the low resistance of the earth wire in part (f).

✅ Correct answer

Swap the blue wire and the green and yellow wire.
The blue wire should go to the neutral pin and the green/yellow wire should go to the earth pin.

💡 Key knowledge

Correct plug wiring is important because each wire has a different job:

• Live carries the alternating potential difference.
• Neutral completes the circuit.
• Earth is a safety wire connected to the case.

🧠 How marks are awarded

This is a 1-mark recall question. You only need the correct change to the wires. A full sentence is not necessary, but the answer must be clear enough to show you know the right terminals.

❌ Common errors

• Saying “swap the live and neutral” when the diagram actually shows the earth and neutral are in the wrong places.
• Writing only “rewire it correctly” without saying what to change.
• Using the wrong colour names, such as “yellow wire” instead of “green and yellow wire”.

✅ Correct answers

Potential difference = 230 V
Frequency = 50 Hz

💡 Key knowledge

• UK mains electricity is 230 V.
• UK mains frequency is 50 Hz.
• Frequency means the number of cycles per second.

🧠 How to score both marks

These are separate 1-mark parts. You need the correct number and the correct unit each time.

❌ Common errors

• Writing 240 V instead of 230 V.
• Writing 50 V or forgetting the unit.
• Putting Hz for voltage or V for frequency.

✅ Correct answer

0 V

💡 Key knowledge

The neutral wire and earth wire are both at about the same potential, so there is no potential difference between them.

🧠 Exam tip

When the question asks for a value only, give the value exactly: 0 V. Don’t explain unless asked.

❌ Common errors

• Answering 230 V because of the mains supply.
• Writing 0 without the unit.
• Confusing current with potential difference.

✅ Correct answer

Draw the fuse symbol: a small rectangle in the wire line, as used in circuit diagrams.

What to draw: a straight wire with a small rectangular box around part of the line, matching the standard GCSE circuit symbol.

💡 Key knowledge

A fuse is a safety device. It melts if the current is too large, breaking the circuit.

🧠 How marks are awarded

This is a drawing mark. The symbol must be recognisable and placed in the line of the circuit.

❌ Common errors

• Drawing a bulb, resistor, or switch instead of a fuse.
• Putting the symbol off the line rather than in the circuit line.
• Drawing something too messy to recognise.

✅ Correct answer

The person could get an electric shock because there would be a current through the person.

💡 Key knowledge

• If the live wire touches the metal case, the case can become live.
• If the case is not earthed, touching it can provide a path to earth through the body.
• Current through the body is what makes electric shocks dangerous.

🧠 What the examiner wanted

For 2 marks, you needed:

• the person could get an electric shock / be electrocuted;
• because current flows through the person / there is a potential difference across the person.

❌ Common errors

• Saying only “it is dangerous” without explaining why.
• Talking about the plug fuse instead of the person.
• Saying “the person gets electricity” instead of current flows through the person.

✅ Correct answer

The charge flows through the earth wire instead of the person, because the earth wire has a much lower resistance than a person.

💡 Key knowledge

• The earth wire provides a safe path for current.
• Because its resistance is low, current takes that path instead of through the body.
• This can also cause the fuse to melt and break the circuit.

🧠 Full-mark answer structure

To get 2 marks, include both ideas:

1. current flows through the earth wire, not the person;
2. the earth wire has lower resistance / the fuse may blow so the case does not stay live.

📐 Not a calculation, but a cause-and-effect chain

Fault: live wire touches metal case
Then: current flows to earth through the earth wire
Result: the case is kept safe / the fuse breaks the circuit

❌ Common errors

• Only saying “it is safe” with no explanation.
• Writing that the earth wire “stops electricity” — it actually gives a safe route.
• Forgetting to mention lower resistance, which is the key reason the current goes through the earth wire.

💡 Remember these facts

• Brown = live
• Blue = neutral
• Green/yellow = earth
• UK mains = 230 V, 50 Hz
• Neutral-earth potential difference = 0 V

🧠 Best exam habit

In safety questions, always connect the idea of a fault to the current path and then to the safety outcome. That is what earns explanation marks.