IGCSE · 4 · structured
Electricity and magnetism · Question 8
Electricity and magnetism · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- discriminating
- Marks
- 9
- Topics
- 1
- Answer
- Complete
A bar magnet is pushed, north pole first, into a coil of insulated wire connected to a sensitive centre-zero ammeter. The ammeter needle deflects to the right while the magnet is moving in.
- (a)
State State what happens to the ammeter reading while the magnet is held stationary inside the coil.
1 mark - (b)
Explain Explain, in terms of magnetic field lines, why a current is produced only while the magnet is moving.
3 marks - (c)
State State two changes to the experiment that would each increase the size of the deflection.
2 marks - (d)
Explain The magnet is now pulled out of the coil, south pole first, at the same speed. Explain what is observed on the ammeter, and why.
3 marks
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(a)
State State what happens to the ammeter reading while the magnet is held stationary inside the coil.
Answer the command word directly and use precise physical vocabulary. Include only the distinct features or facts that earn marks, without burying them in unrelated background information.
- 1
the reading returns to (and stays at) zero
(b)
Explain Explain, in terms of magnetic field lines, why a current is produced only while the magnet is moving.
State the outcome first, then link cause to effect with the relevant physical principle. Each link in the reasoning should be explicit enough to earn its own marking point.
- 1
an e.m.f. is induced when the magnetic field lines linking the coil change
- 2
moving the magnet changes the number of field lines through the coil, cutting the turns of wire
- 3
a stationary magnet gives an unchanging field through the coil, so no e.m.f. and no current
(c)
State State two changes to the experiment that would each increase the size of the deflection.
Answer the command word directly and use precise physical vocabulary. Include only the distinct features or facts that earn marks, without burying them in unrelated background information.
- 1
move the magnet faster
- 2
any one of: use a stronger magnet; use a coil with more turns; use a coil of smaller cross-sectional area wound closer to the magnet
(d)
Explain The magnet is now pulled out of the coil, south pole first, at the same speed. Explain what is observed on the ammeter, and why.
State the outcome first, then link cause to effect with the relevant physical principle. Each link in the reasoning should be explicit enough to earn its own marking point.
- 1
the needle deflects to the left — the current is in the opposite direction
- 2
because the field through the coil is changing in the opposite sense as the magnet is withdrawn
- 3
the size of the deflection is the same, because the rate of change of the field is the same
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