IGCSE Physics / Magnetism and electromagnetism
Magnetically hard and soft materials
Edexcel International GCSE Physics (4PH1), chapter 20: Magnetism and electromagnetism, specification point 6.3. Free lesson.
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Magnetically hard and soft materials differ in how easily they magnetise and whether they keep their magnetism. This helps you choose the right material for permanent magnets, electromagnets and transformer cores.
How hard and soft materials behave
These terms describe how a material behaves in a magnetic field, not how hard it feels to touch. Steel is the usual magnetically hard material, while iron is the usual magnetically soft material. A magnetically hard material is difficult to magnetise, but keeps its magnetism once magnetised. A magnetically soft material is easy to magnetise, but loses its magnetism when the field is taken away. Steel is used for permanent magnets. Iron is used for electromagnet and transformer cores.
How to tell iron and steel apart
Both rods become magnetised when held against a magnet, so both can pick up paper clips. The difference appears when the magnet is removed.
Choosing a material for a job
Ask whether the material needs to keep its magnetism. If it must stay magnetised, choose a hard material. If it needs to lose its magnetism, choose a soft material. A fridge magnet must stay magnetised for years, so it uses a hard material such as steel. A crane electromagnet must let go when the current stops, so its core uses soft iron. A transformer core's magnetism reverses many times a second, so it also uses soft iron.
Explain why a crane uses iron
For a three-mark explanation, give the material's magnetic property, describe what happens when the current changes, then link that behaviour to the crane's job. Iron is magnetically soft. It magnetises easily when the current is on and loses its magnetism when the current is switched off. The crane can then drop the car. A steel core would stay magnetised and keep holding it.
Why a permanent magnet uses steel
A permanent magnet needs to stay magnetised. Steel does this because it is magnetically hard, while iron loses its magnetism when the magnetic field is removed. Steel is hard to magnetise, but once magnetised it keeps its magnetism. Iron would lose its magnetism straight away.