A student places a soft iron bar inside a solenoid connected to a battery. Explain why the soft iron bar becomes a magnet when the current is switched on, and describe what happens to the magnetism of the soft iron bar when the current is switched off.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
The solenoid carries a current, so it produces a magnetic field inside the coil.
The magnetic field of the solenoid magnetises the soft iron bar, causing it to become a magnet.
Soft iron is a magnetically soft material, meaning it is easy to magnetise.
When the current is switched off, the magnetic field of the solenoid disappears.
The soft iron bar loses its magnetism almost immediately because it is a magnetically soft material.
The magnetic field of the solenoid magnetises the soft iron bar, causing it to become a magnet.
Soft iron is a magnetically soft material, meaning it is easy to magnetise.
When the current is switched off, the magnetic field of the solenoid disappears.
The soft iron bar loses its magnetism almost immediately because it is a magnetically soft material.
Examiner tips
- Use the word "magnetises" to show understanding of the process. Show the cause–effect chain: current → field → magnetisation → field disappears → demagnetisation. Mention that soft iron is easy to magnetise and demagnetise.
Common mistakes
- Forgetting to state that the solenoid’s field magnetises the bar. Claiming the bar remains magnetised after the current is off. Using vague terms like "magnetic material" without specifying soft iron’s properties.
Mark scheme (5 marks)
- The solenoid carrying a current produces a magnetic field (inside the coil)
- The magnetic field of the solenoid magnetises the soft iron bar / causes the soft iron bar to become a magnet
- Soft iron is a magnetically soft material, meaning it is easy to magnetise
- When the current is switched off, the magnetic field of the solenoid disappears
- The soft iron bar loses its magnetism (almost immediately) when the current is switched off, because it is a magnetically soft material
Key terms in this question
Related
- All WJEC A-Level Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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