AQA GCSE Combined Science: Trilogy Physics Paper 2 (Foundation), November 2021: Question 2

✅ Correct Answer

First box ticked:

💡 Key Knowledge

• Magnetic field lines never cross each other.
• Arrows on magnetic field lines always show the direction of the force on a free north pole, meaning lines always point out of North and into South.
• Lines are closest together at the poles, showing where the magnetic field is strongest.

❌ Common Errors

• Selecting the 3rd diagram where arrows point backwards (from South to North).
• Selecting the 2nd or 4th diagram where the field pattern shows two separate butterfly-like loops per pole rather than loops linking N to S.

✅ Correct Answer

The iron bar should be labelled with:

N on the left-hand end (closest to the permanent magnet's S pole) and S on the right-hand end.

💡 Key Knowledge

• When an unmagnetised magnetic material (such as iron) is placed in a magnetic field, it becomes an induced magnet.
• Opposite poles attract: therefore, the end nearest to the permanent magnet's South pole develops an induced North pole.

🧠 Exam Technique

Remember: "Opposites attract." Since the iron bar is drawn towards the permanent magnet, the side closest must be the opposite pole to the one facing it.

✅ Correct Answer

Tick box 2:

"The iron bar experiences a magnetic force of attraction."

💡 Key Knowledge

• Induced magnetism always causes attraction, never repulsion!
• If you flip the permanent magnet so its North pole faces the iron bar, the left end of the iron bar simply becomes an induced South pole. Opposite poles still face each other, so it still attracts.

❌ Common Errors

Many students instinctively tick "experiences a magnetic force of repulsion", mistakenly treating the iron bar as a permanent magnet with fixed poles. Iron loses its magnetism once removed, and its induced poles simply flip when the field flips.

✅ Correct Answer

• Nickel [1 mark]
• Steel [1 mark]

💡 Key Knowledge

Only four common engineering metals are magnetic elements/alloys at room temperature:

• Iron (pure element)
• Steel (alloy containing mostly iron)
• Nickel (pure element)
• Cobalt (pure element)

Aluminium, copper, and magnesium are non-magnetic metals and will not be attracted to a magnet.

🧠 Exam Technique

The question specifies two boxes. Always read the instructions carefully—ticking more than two can forfeit your marks!

✅ Correct Answer

Tick box 2:

"An electromagnet can be switched on and off."

💡 Key Knowledge

• A permanent magnet is always magnetic, which makes dropping or releasing separated scrap metal impossible.
• An electromagnet produces a magnetic field only when electric current flows. By turning the switch off, the magnetic field disappears and the attracted metal drops cleanly into a collection hopper.

❌ Common Errors

Assuming electromagnets attract different metals (e.g. copper or aluminium). Both permanent magnets and electromagnets can only attract magnetic materials.

✅ Correct Answers

02.6: "The iron nail makes the magnetic field stronger." [1 mark]

02.7: "Use a greater current." [1 mark]

💡 Key Knowledge

To increase the strength of an electromagnet, you can:

• Increase the current flowing through the wire.
• Add more turns of wire to the coil.
• Add a soft iron core (like the iron nail), which becomes magnetised and dramatically intensifies the magnetic field inside the coil.

🧠 Exam Technique

• Thinner wire increases electrical resistance, which actually reduces the current and weakens the magnet.
• A shorter nail provides less core material for the coil, which does not increase strength.