Magnetism and electromagnetism — AQA GCSE Physics revision

Magnets and magnetic fields

• Magnets have two poles, north and south; like poles repel, unlike poles attract.
• A magnetic field is the region around a magnet where a magnetic material experiences a force; field lines point from north to south outside the magnet.
• Field strength is greatest where field lines are closest together, such as near the poles.
• Induced magnets are magnetic materials (e.g. iron, steel) that become magnets when placed in a magnetic field, but lose most of their magnetism when removed from it.
• Permanent magnets produce their own field and keep their magnetism.

Electromagnetism

• A current-carrying wire produces a magnetic field around it; the field forms concentric circles, and its direction can be found with the right-hand grip rule.
• Shaping a wire into a coil (solenoid) concentrates the field lines to make a stronger, more uniform field inside, similar to a bar magnet.
• An electromagnet is a solenoid often wrapped around an iron core, which strengthens the field; electromagnets can be switched on and off, unlike permanent magnets.
• The strength of an electromagnet's field increases with current and with the number of turns on the coil.

Key terms

Magnetic field

Region around a magnet where a magnetic material experiences a force.

Induced magnetism

Temporary magnetism gained by a material in a magnetic field.

Solenoid

A coil of wire that produces a strong, uniform magnetic field when carrying current.

Electromagnet

A magnet whose field is produced by an electric current, often with an iron core.

Motor effect

The force on a current-carrying conductor in a magnetic field.

Fleming's left-hand rule

A rule using thumb, first and second fingers to find force, field and current directions.

Common exam traps

• Mixing up the right-hand grip rule (for field around a wire) with Fleming's left-hand rule (for force/motor effect).
• Thinking induced magnets keep their magnetism permanently — they lose most of it once removed from the field.
• Forgetting that magnetic field lines go from north to south outside the magnet.

Practice questions with answers

1. 1. Like magnetic poles will:

   • • Attract
   • • Repel
   • • Have no effect
   • • Cancel out

   Answer: Repel

   Like poles (N-N or S-S) repel; unlike poles (N-S) attract.

2. 2. Magnetic field lines point from:

   • • South to north outside the magnet
   • • North to south outside the magnet
   • • Always downward
   • • Randomly in all directions

   Answer: North to south outside the magnet

   By convention, field lines leave the north pole and enter the south pole outside the magnet.

3. 3. Where is a magnetic field strongest?

   Answer: Where field lines are closest together

   Field strength corresponds to field line density — closer lines mean a stronger field, usually near the poles.

4. 4. What is an induced magnet?

   • • A magnet that always stays magnetic
   • • A material that becomes magnetic temporarily in a field
   • • A magnet made only from steel
   • • A type of electromagnet with no current

   Answer: A material that becomes magnetic temporarily in a field

   Induced magnets, like iron in a magnetic field, lose most magnetism once the field is removed.

5. 5. What shape does the magnetic field take around a straight current-carrying wire?

   • • Straight lines
   • • Concentric circles
   • • Random
   • • Parallel lines

   Answer: Concentric circles

   The field around a straight wire forms concentric circles centred on the wire.

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