Magnetism

What is Magnetism?

Magnetism is a non-contact force exerted by magnets on certain materials and on other magnets. It can attract or repel without any physical contact between objects.

Magnetism arises from the movement of electrons within atoms. In magnetic materials, groups of atoms called magnetic domains all align in the same direction, creating a net magnetic effect.

Poles and Rules

Every magnet has two poles: a North (N) pole and a South (S) pole. The fundamental rule of magnetism is:

Like poles repel; unlike poles attract.

• N and N → repel (force pushes them apart)
• S and S → repel
• N and S → attract (force pulls them together)

You cannot isolate a single magnetic pole. If you cut a magnet in half, each piece has its own N and S pole.

Magnetic Materials

Not all materials are attracted to magnets. Only ferromagnetic materials are:

Material	Type	Notes
Iron	Temporary magnet	Easy to magnetise and demagnetise; used in electromagnet cores
Steel	Permanent magnet	Hard to magnetise but retains magnetism; used in bar magnets
Nickel	Magnetic	Used in some alloys
Cobalt	Magnetic	Used in high-performance magnets

Non-magnetic materials: copper, aluminium, plastic, wood, glass, gold, silver.

A simple test: bring a magnet near the material. Attraction confirms it is magnetic (but does not tell you if it is itself a magnet — you need to test both poles to confirm magnetism vs. induction).

Magnetic Fields

A magnetic field is the region around a magnet where magnetic forces act on other magnets or magnetic materials. Magnetic fields are represented by field lines:

• Field lines run from the North pole to South pole outside the magnet
• Inside the magnet, field lines run from South to North (completing the loop)
• Closer field lines = stronger magnetic field
• The direction of the field line shows which way a free North pole would move

The strongest parts of a bar magnet are at its poles — field lines are most concentrated there.

Plotting Magnetic Fields

To plot a magnetic field:

1. Place a bar magnet on paper
2. Put a compass near one pole
3. Mark where the compass needle points
4. Move the compass to the new position and repeat
5. Join the dots to trace a field line

Induced Magnetism

When a ferromagnetic material (like iron) is placed near a magnet, its magnetic domains align with the external field — the material becomes temporarily magnetised. This is called induced magnetism.

Key point: the induced pole nearest to the magnet is always opposite to the magnet's pole — so induction always results in attraction, never repulsion.

When the external magnet is removed, a temporary magnet (like iron) loses its magnetism quickly. A permanent magnet (like steel) retains it.

Electromagnets

An electromagnet is produced by passing an electric current through a solenoid (coil of wire). The current creates a magnetic field around the wire; coiling the wire concentrates and strengthens the field.

How to increase electromagnet strength:

• Increase the current flowing through the wire
• Increase the number of turns of wire in the coil
• Add a soft iron core inside the coil (this concentrates the magnetic field)

Advantages of electromagnets over permanent magnets:

• Can be switched on and off
• Strength can be varied by changing the current
• Polarity can be reversed by reversing the current

Applications of electromagnets:

• Electric motors
• Loud speakers
• MRI (Magnetic Resonance Imaging) scanners
• Electric bells and buzzers
• Scrapyard cranes (lifting and releasing scrap metal)
• Maglev (magnetic levitation) trains

Demagnetising a Magnet

A permanent magnet can be demagnetised by:

• Heating it — thermal energy disrupts domain alignment
• Hammering it repeatedly
• Passing alternating current through a coil surrounding it (demagnetising coil)

Key Terms

• Magnet — object that produces a magnetic field
• Magnetic pole — the point on a magnet where the field is strongest (N or S)
• Magnetic field — the region around a magnet where forces act
• Ferromagnetic — a material that can be strongly magnetised (iron, steel, nickel, cobalt)
• Induced magnetism — temporary magnetism produced in a material by a nearby magnet
• Solenoid — a coil of wire that acts as an electromagnet when current flows
• Domain — a region in a magnetic material where all atoms are aligned the same way

Common Mistakes

• Thinking all metals are magnetic — only iron, steel, nickel, and cobalt are ferromagnetic; copper and aluminium are not
• Saying a compass needle is attracted to the North Pole of Earth — a compass North seeks Earth's geographic North, which is actually a magnetic South pole
• Confusing field line direction: lines go from North to South outside the magnet, not the other way
• Thinking cutting a magnet in half removes one pole — it creates two smaller complete magnets

Tips and Tricks

• Like poles Repel — both words start with a vowel sound? No — use the rhyme: "Unlike poles attract, like poles fight back"
• Field lines never cross — if they did, the field would have two directions at the same point, which is impossible
• To identify which end of an unmarked magnet is N or S: hang it freely — it will align with Earth's field, North end pointing roughly North
• More coils + more current + iron core = strongest electromagnet — all three together give maximum effect