Compare temporary soft-iron and permanent steel magnets
Choose a magnetic material by how readily it magnetises and how well it retains magnetisation.
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Describe induced magnetism.
- Distinguish magnetisation from hardness in everyday language.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What property helps a switched magnetic lifter release its load?
What you will learn
- Compare temporary soft-iron and permanent steel magnets.
- Select a material for retaining or releasing an object.
Compare acquisition and retention
Soft iron is readily magnetised and readily loses much of its magnetisation when the magnetising influence is removed. It suits a temporary magnet such as the core of a switched electromagnet. Steel is harder to magnetise but retains magnetisation better, making it suitable for the syllabus permanent-magnet model.
'Harder to magnetise' concerns the magnetic response, not a requirement to hit the material or a claim about a measured mechanical hardness. 'Permanent' means useful retained magnetisation; it does not promise a magnet can never be weakened by temperature, impacts or other magnetic influences.
Choose for the desired behaviour
A device that must release a magnetic load when its current is switched off benefits from a soft-iron core. A compass needle or latch that must remain magnetic without a continuing current needs a suitable permanent magnet. Link the choice to the required retention rather than simply naming a metal.
Compare materials under the same magnetising and removal conditions if given experimental evidence. A stronger field during one trial can confound a material comparison. This lesson gives qualitative properties, not a universal numerical retention percentage.
Sources for this lesson
Pause and explain
Which choice suits a magnet that should remain magnetised without a continuous current?
Worked example
Choose a core for a crane electromagnet that should release its load when switched off.
Show the worked solution
- The core should be magnetised during operation.
- It should retain little magnetism after switching off.
- Soft iron has the required temporary response.
Answer Soft iron, because it readily magnetises and readily loses much of that magnetisation.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Compare soft iron and steel after the magnetising influence is removed.
Give me a hint
Describe retained magnetisation, not just initial attraction.
Compare my reasoning
- Soft iron loses much of its magnetism readily.
- Steel retains magnetisation better.
- They suit temporary and permanent roles respectively.
Soft iron: temporary; steel: better retention for permanent magnets.
Look for these in your work
- State both materials.
- Connect the names to retention.
Explain a suitable material choice for a compass needle that needs lasting magnetisation.
Give me a hint
The needle should remain a magnet without a powered inducing coil.
Compare my reasoning
- The needle needs retained poles.
- A suitable permanent-magnet material retains magnetisation.
- Steel fits the stated comparison.
Steel in this model, because it retains magnetisation.
Look for these in your work
- Name the required property.
- Avoid treating every metal as equivalent.
Steel was tested with a strong magnet and iron with a weak one. Does the observed lifting difference isolate retention?
Give me a hint
Check whether the magnetising conditions were comparable.
Compare my reasoning
- The source fields differed.
- The initial magnetisation may therefore differ.
- A controlled comparison must match the magnetising and removal conditions.
No; unequal magnetising conditions confound the material comparison.
Look for these in your work
- Identify the changed condition.
- Describe a fairer comparison.
Common mistakes
- Retained magnetisation and ease of magnetising are different.
- Permanent does not mean impossible to weaken.
- Compare matched conditions.
What can you explain now?
Which listed material better retains magnetisation after the inducing field is removed?
Compare with the explanation
Steel.
The syllabus contrasts permanent steel magnets with temporary soft-iron magnets.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Choose temporary or permanent material by magnetisation and retention properties.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.