Magnets and Magnetic Fields

This lesson covers permanent magnets, induced magnets, magnetic poles, the forces between them and how to map magnetic fields using field lines, as required by the Edexcel GCSE Combined Science specification (1SC0). A solid understanding of basic magnetism is essential before tackling electromagnets and the motor effect.

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Magnetic Materials

Only a few materials are magnetic — they are attracted to magnets. The three magnetic elements you must know are:

Magnetic Element	Symbol
Iron	Fe
Cobalt	Co
Nickel	Ni

Steel (an alloy containing iron) is also magnetic.

Exam Tip: Copper, aluminium, gold and silver are not magnetic. A very common trick question asks whether all metals are magnetic — they are not.

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Permanent and Induced Magnets

Feature	Permanent Magnet	Induced Magnet
Produces its own magnetic field?	Yes — at all times	Only when placed in a magnetic field
Keeps its magnetism?	Yes — indefinitely	No — loses it when removed from the field
Example	Bar magnet, horseshoe magnet	An iron nail attracted to a permanent magnet

How Induced Magnetism Works

When a magnetic material (e.g. a piece of iron) is placed inside a magnetic field, the magnetic domains inside the material line up with the external field. The material temporarily becomes a magnet itself. The end of the material nearest the magnet's north pole becomes a south pole (so it is attracted).

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Magnetic Poles

Every magnet has two poles — a north-seeking pole (N) and a south-seeking pole (S). The magnetic field is strongest at the poles.

The Law of Magnetism

Combination	Result
N — N	Repulsion
S — S	Repulsion
N — S	Attraction

Exam Tip: Repulsion is the only sure test for a magnet. Attraction could be caused by an induced magnet (e.g. an unmagnetised piece of iron will always be attracted to a magnet). Only two magnets can repel each other.

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Magnetic Fields

A magnetic field is the region around a magnet where a magnetic force acts on another magnetic material or magnet. You cannot see a magnetic field, but you can represent it with field lines.

Properties of Magnetic Field Lines

• Field lines go from north to south (outside the magnet).
• The lines never cross.
• Where the lines are closer together, the field is stronger.
• Where the lines are further apart, the field is weaker.

graph LR
    subgraph "Bar Magnet Field Pattern"
    direction LR
    N["N pole"] -->|"Field lines curve outward"| S["S pole"]
    end

The field is strongest at the poles (lines are closest together) and weakest further from the magnet.

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Plotting a Magnetic Field with a Compass

Method

1. Place a bar magnet on a sheet of paper and draw around it.
2. Place a plotting compass near the north pole of the magnet.
3. Mark the position of both ends of the compass needle with a dot.
4. Move the compass so that the tail of the needle sits on the dot just made for the head.
5. Mark the new position of the head with another dot.
6. Repeat until the trail of dots reaches the south pole (or runs off the paper).
7. Join the dots to form a smooth field line and add an arrow from N to S.
8. Repeat for several different starting positions around the magnet.

What the Compass Shows

The compass needle is itself a tiny magnet. Its north pole always points in the direction of the magnetic field — that is, away from the north pole of the bar magnet and towards the south pole.

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Uniform and Non-Uniform Fields

Type	Description	Where Found
Uniform field	Field lines are parallel and equally spaced; field strength is the same everywhere	Between two flat, opposite magnetic poles
Non-uniform field	Field lines are curved and/or vary in spacing	Around a bar magnet

A uniform field exists between two flat, opposite poles placed close together (e.g. between the N and S faces of two bar magnets). The field lines are straight, parallel and evenly spaced.

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The Earth's Magnetic Field

The Earth behaves as though it contains a giant bar magnet. The geographic North Pole is near a magnetic south pole (which is why the north-seeking pole of a compass points towards geographic north).

Feature	Detail
Shape	Similar to a bar magnet field
Cause	Convection currents in the molten iron outer core
Use	Allows navigation with a compass

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Worked Example

A student places two bar magnets end to end on a table, with a north pole facing a south pole. Describe the field pattern between the magnets.

The field lines run in straight, parallel lines from the north pole of one magnet to the south pole of the other. The lines are equally spaced (approximately), showing the field between the poles is roughly uniform.

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Common Misconceptions

Misconception	Correction
All metals are magnetic	Only iron, cobalt, nickel (and their alloys) are magnetic
Attraction proves an object is a magnet	Attraction could be induced magnetism; only repulsion proves both objects are magnets
Field lines start at south and end at north	Field lines go from north to south (outside the magnet)
A compass needle points to a magnetic north pole	A compass north-seeking pole is attracted to the Earth's magnetic south pole, which is near the geographic North Pole

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Summary

• Magnetic materials: iron, cobalt, nickel (and alloys like steel).
• Permanent magnets produce their own field; induced magnets are temporary.
• Like poles repel; unlike poles attract. Repulsion is the only sure test for a magnet.
• Magnetic field lines go from north to south, never cross, and are closer together where the field is stronger.
• A plotting compass can be used to trace field lines around a bar magnet.
• A uniform field has parallel, equally spaced field lines (found between two opposite flat poles).
• The Earth has a magnetic field similar to a bar magnet, enabling compass navigation.

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Deeper Dive: Magnetic Domains

Every piece of iron, cobalt or nickel is made up of countless tiny regions called magnetic domains. Each domain behaves like a microscopic magnet with its own north and south pole. In an unmagnetised piece of iron, these domains point in many different directions, so their individual fields cancel out — the iron produces no net magnetic field.

When an external magnetic field is applied (for example, by placing the iron next to a bar magnet), the domains begin to rotate and align with the external field. The more domains that align, the stronger the induced magnetism becomes. If every domain aligns fully, the material has reached magnetic saturation — it cannot be magnetised any more strongly.

State	Domain Alignment	Net Field
Unmagnetised	Random directions	Zero
Partially magnetised	Some aligned	Weak
Fully magnetised (saturated)	All aligned	Strongest possible

In soft magnetic materials (like soft iron), the domains return to random orientations as soon as the external field is removed — the material loses its magnetism. In hard magnetic materials (like steel), the domains stay locked in place, which is how permanent magnets are made.

Making and Destroying Magnets

Method to Make a Magnet	Method to Destroy a Magnet
Stroke a steel bar repeatedly with one pole of a magnet	Heat the magnet above its Curie temperature
Place the steel inside a solenoid carrying a DC current	Hit it repeatedly with a hammer
Leave the steel aligned in Earth's field for a long time	Place it in a strong AC field that randomises the domains

Heating or hammering a magnet adds enough energy for the domains to jiggle out of alignment, which is why dropped or heated magnets often weaken.

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Worked Example 2: Testing an Unknown Bar

A student is given two identical-looking metal bars. One is a permanent magnet; the other is an unmagnetised piece of iron. Without any other equipment, how can the student decide which is which?

Bring the two bars close together in several orientations:

• If, in any orientation, the bars repel each other, both must be permanent magnets — but we only have one magnet here, so repulsion will never occur in this scenario.
• If the bars always attract each other no matter which ends face each other, then one is a permanent magnet and the other is an unmagnetised iron bar (the iron becomes induced, and attraction happens from either end).

The permanent magnet can be identified as the bar that, when brought near a small iron object (e.g. a paperclip), picks it up from its poles most strongly. The iron bar only picks up the paperclip if it is itself placed near the permanent magnet first (induction).

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Exam-Style Question Breakdown

Question: Describe the magnetic field around a bar magnet and explain how you would use a plotting compass to confirm your description. (6 marks)

A good answer should include:

1. Field shape — lines curve from the north pole round to the south pole outside the magnet (1 mark).
2. Field strength variation — lines are closer together near the poles where the field is strongest (1 mark).
3. Direction — field lines have arrows pointing from N to S (1 mark).
4. Method — place the compass near the north pole and mark both ends of the needle (1 mark).
5. Repeat — move the compass so the tail sits where the head was, mark again, and repeat to build up a trail (1 mark).
6. Complete line — join the dots with a smooth curve and add an arrow from N to S; repeat from several starting points (1 mark).

Answering at different grade levels

The same topic can be answered at different depths. Compare these two responses to "Describe a magnetic field around a bar magnet."

Grade 3–4 response: "A magnetic field is the space around a magnet. The field lines go from north to south. They are stronger at the poles."

This answer uses some correct vocabulary but mixes colloquial phrasing with the required terms. It does not distinguish permanent vs induced magnets, does not mention that magnetic field lines never cross, and uses vague language like "stronger" without linking it to line spacing.

Grade 7–9 response: "The magnetic field surrounding a permanent bar magnet is a non-uniform three-dimensional region in which a magnetic force acts on another magnetic pole. The field is represented by magnetic field lines that emerge from the north-seeking pole, curve around the outside of the magnet, and enter the south-seeking pole. Field lines never cross (since at any point the field has only one direction) and their density represents field strength — where the lines are closer together, near the poles, the field is strongest. A plotting compass aligns with the field because it is a small permanent magnet and experiences a turning force. By contrast, an unmagnetised iron nail placed nearby would become an induced magnet only temporarily, losing its magnetism once removed from the field."

The Grade 7–9 answer uses precise terms — magnetic field lines, permanent vs induced magnet, non-uniform field — and explains why the field lines never cross and why the compass works. It shows the distinction between permanent and induced magnetism without being prompted.

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Edexcel alignment: This content is aligned with Edexcel GCSE Combined Science (1SC0) Physics Topic 9 Magnetism / Topic 10 The Universe (Astronomy is Combined-only includes solar system, life cycle of stars) — specifically CP10 Magnetism (permanent and induced magnets, magnetic poles, magnetic fields, plotting compasses, Earth's magnetic field). Assessed on Physics Papers 1 and 2.