Permanent and Induced Magnets

In this lesson you will learn the difference between permanent magnets and induced magnets, and explore how materials can be classified as magnetically hard or magnetically soft. This maps to AQA GCSE Combined Science Trilogy (8464) specification section 6.7.1 — Permanent and induced magnetism, magnetic forces and fields.

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Permanent Magnets

A permanent magnet produces its own magnetic field. It does not need an external source of energy or another magnetic field to be magnetic.

Properties of Permanent Magnets

• Always have a north pole and a south pole.
• Produce a magnetic field at all times.
• Made from magnetically hard materials (e.g. steel, alnico, neodymium).
• Retain their magnetism for a very long time.
• Examples: bar magnets, horseshoe magnets, fridge magnets.

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Induced Magnets

An induced magnet is a material that becomes magnetic only when it is placed in a magnetic field. When the external field is removed, the induced magnet loses most or all of its magnetism.

Properties of Induced Magnets

• Only magnetic when inside an external magnetic field.
• Lose magnetism when the external field is removed.
• The nearest pole of an induced magnet is always opposite to the pole of the permanent magnet that is inducing it.
• As a result, induced magnets are always attracted to the permanent magnet — they never repel.

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Permanent vs Induced Magnets — Comparison Table

Feature	Permanent Magnet	Induced Magnet
Source of magnetism	Own internal magnetic field	External magnetic field
Retains magnetism?	Yes — always magnetic	No — loses magnetism when field removed
Poles	Fixed N and S	Temporary; nearest pole is always opposite to the inducing magnet
Force with a permanent magnet	Can attract OR repel	Always attracts
Material type	Magnetically hard	Magnetically soft
Examples	Bar magnet, horseshoe magnet	Iron nail near a magnet, paper clip in a magnetic field

Exam Tip: A key AQA exam point: induced magnets are always attracted to the permanent magnet that is inducing them. They can never repel. This is because the nearest pole of the induced magnet is always the opposite pole to the permanent magnet.

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Magnetically Hard and Magnetically Soft Materials

Material Type	Easy to Magnetise?	Retains Magnetism?	Use
Magnetically hard (e.g. steel)	Difficult	Yes — retains well	Permanent magnets
Magnetically soft (e.g. iron)	Easy	No — loses quickly	Electromagnets, temporary/induced magnets

Why Does This Matter?

• Steel is used for permanent magnets because it is hard to demagnetise once magnetised.
• Iron is used for electromagnets and transformer cores because it can be magnetised and demagnetised rapidly (switches on and off easily).

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How to Magnetise and Demagnetise

Magnetising

1. Stroking — repeatedly stroke an iron or steel bar with one pole of a permanent magnet, always in the same direction.
2. Solenoid method — place the material inside a solenoid carrying a direct current. The magnetic field of the solenoid magnetises the material.

Demagnetising

1. Heating — heating a magnet above its Curie temperature disrupts the alignment of magnetic domains.
2. Hammering — physically striking the magnet disrupts domain alignment.
3. Alternating current in a solenoid — placing the magnet in a solenoid carrying an alternating current that gradually decreases to zero.

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Magnetic Domains (Extension)

Inside a magnetic material, atoms behave like tiny magnets. Groups of atoms align in the same direction to form regions called magnetic domains.

• In an unmagnetised material, domains point in random directions — their fields cancel out.
• In a magnetised material, domains are aligned — their fields add up to produce an overall magnetic field.

graph LR
    subgraph "Unmagnetised Material"
        D1["→"] --- D2["↑"] --- D3["←"] --- D4["↓"]
    end
    subgraph "Magnetised Material"
        D5["→"] --- D6["→"] --- D7["→"] --- D8["→"]
    end

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Worked Example

Q: A student holds a permanent bar magnet near an iron nail. The nail is attracted and sticks to the magnet. The student then removes the magnet. Explain what happens to the nail.

A: When the permanent magnet is brought close, the iron nail becomes an induced magnet. The magnetic domains inside the nail align with the external field. The nearest end of the nail becomes the opposite pole to the permanent magnet, so the nail is attracted. When the permanent magnet is removed, the iron nail loses most of its magnetism because iron is a magnetically soft material — its domains return to random orientations.

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Common Mistakes

Mistake	Correction
"Induced magnets can repel permanent magnets"	Induced magnets are always attracted
"Iron is used for permanent magnets"	Iron is magnetically soft — steel is used for permanent magnets
"Demagnetising means destroying the material"	Demagnetising simply randomises the domains

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Summary

• Permanent magnets produce their own magnetic field and retain it indefinitely.
• Induced magnets are only magnetic when in an external field and always attract the inducing magnet.
• Magnetically hard materials (steel) retain magnetism — used for permanent magnets.
• Magnetically soft materials (iron) lose magnetism easily — used for electromagnets.
• Magnetisation aligns magnetic domains; demagnetisation randomises them.

Exam Tip (AQA 8464): Questions on permanent vs induced magnets are very common. Always state that induced magnets lose their magnetism when the field is removed and that they always attract the permanent magnet.

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Why Induced Magnets Always Attract — Detailed Reasoning

A key exam point is being able to explain, not just state, why induced magnets can never repel a permanent magnet. The logic chain is as follows: