AQA GCSE Combined Science: Trilogy Physics Paper 2 (Higher), 2024: Question 4

✅ Correct answer

Into the page

1 mark for the correct direction only.

💡 Key knowledge

• Magnetic field lines go from N to S.
• The current in the wire is upwards.
• Use the motor effect / Fleming’s left-hand rule to find the force.
• For this arrangement, the force is into the page.

🧠 Exam technique

• Do not guess left/right without checking the field direction.
• If the question shows a diagram, picture the current, field, and force as a three-way relationship.
• For a 1-mark direction question, you only need the final direction, not an explanation.

❌ Common errors

• Writing to the left or to the right instead of into/out of the page.
• Mixing up the direction of the magnetic field.
• Using the wrong hand rule or reversing the current and field.

📐 Calculation steps

1. Write the equation: F = BIL
2. Rearrange: B = F / (IL)
3. Convert the length into metres: 80 mm = 0.080 m
4. Substitute the values: B = 0.092 / (4.6 × 0.080)
5. Calculate: B = 0.092 / 0.368 = 0.25
6. Give the unit: tesla (T)

✅ Correct answer

Magnetic flux density = 0.25 T

Marks are awarded for: correct equation, rearrangement, correct substitution/calculation, and unit.

💡 Key knowledge

• Use the motor effect equation: F = BIL
• B = magnetic flux density
• I = current in amperes (A)
• L = length of wire in the magnetic field, in metres (m)
• F = force in newtons (N)
• Unit of magnetic flux density is tesla (T)

🧠 Exam technique

• Always convert mm to m before calculating unless the question clearly says otherwise.
• Write the equation first: this often earns method marks.
• Keep the answer to a sensible number of significant figures. Here, 0.25 is suitable.
• Always include the unit: no unit = lost mark.

❌ Common errors

• Using 80 instead of 0.080 for the wire length.
• Rearranging incorrectly, such as B = F × I × L .
• Leaving out the unit T.
• Forgetting that the question says the wire length is in the field, so use that length only.

✅ Correct answer

Newton’s third law

1 mark for naming the correct law.

💡 Key knowledge

• Newton’s third law says: if one object exerts a force on another, the second object exerts an equal and opposite force back.
• Here, the electromagnet and permanent magnet exert forces on each other as an action-reaction pair.

🧠 Exam technique

• This is a recall question: do not overcomplicate it.
• “Equal and opposite” is the key clue.

❌ Common errors

• Choosing Newton’s first law because the question mentions force.
• Choosing Newton’s second law because “force” and “movement” are both involved.
• Writing just “third law” without Newton’s name may be accepted in some contexts, but the safest response is the full phrase.

✅ Correct answers

Any two of:

• Move the electromagnet closer to the permanent magnet
• Add more turns to the coil
• Increase the current in the coil / electromagnet

2 marks total: 1 mark for each correct change.

💡 Key knowledge

• These changes make the electromagnet stronger, so the force increases.
• Increasing the potential difference across the coil is accepted because it increases current.
• A stronger electromagnet produces a bigger magnetic force.

🧠 Exam technique

• Give two separate changes, not two versions of the same idea.
• Use precise wording: “increase current” is better than “make it stronger”.
• If you say “closer”, make it clear that you are moving the electromagnet closer to the magnet.

❌ Common errors

• Vague answers like “change it” or “make it bigger”.
• Writing “increase the voltage” without linking it to current. The mark scheme allows it only if it clearly means increasing current.
• Repeating the same idea twice, for example “increase current” and “put more power in” if they mean the same thing.

✅ Correct answers

Any two of:

• Reverse the current in the coil / electromagnet
• Turn the electromagnet around to reverse the poles
• Wrap the coil in the opposite direction around the iron core

2 marks total: 1 mark for each correct change.

💡 Key knowledge

• Reversing the current reverses the magnetic field of the electromagnet.
• If the poles reverse, the force direction also reverses.
• The direction of the force depends on the direction of current and magnetic field.

🧠 Exam technique

• For a reversed force, think: reverse current or reverse poles.
• Be careful not to just describe making the electromagnet stronger; that changes magnitude, not direction.

❌ Common errors

• Giving answers that increase force instead of reverse it.
• Saying “change the magnet” without stating how the direction changes.
• Repeating the same idea twice, such as “reverse the current” and “change the current the other way” if the examiner treats them as identical.

💡 Examiner insight

• 04.1: Only the correct direction scored the mark.
• 04.2: Students lost marks most often by not converting 80 mm to 0.080 m .
• 04.3: This was a straightforward recall mark for Newton’s third law.
• 04.4 and 04.5: Best answers were specific and linked to the electromagnet, not just “make it stronger” or “change it”.

🧠 Quick full-marks checklist

• Direction question: use the diagram carefully.
• Calculation: write equation, rearrange, substitute, calculate, add unit.
• Recall question: say the exact law name.
• Explain changes: use precise magnet/electromagnet language.

❌ Biggest traps

• Forgetting unit conversions.
• Not giving units for a calculation answer.
• Confusing stronger force with reversed force.
• Being too vague in 2-mark explanation questions.