GCSE Physics Magnetism & Electromagnetism Notes
Magnets have fields that exert forces; an electric current also makes a magnetic field. Combine the two and you get electromagnets and motors.
Key concepts
- Magnetic field
- The region around a magnet where a force acts on another magnet or magnetic material. Field lines run from north to south and are strongest where they are closest together.
- Permanent vs induced
- A permanent magnet always produces its own field; an induced magnet only becomes magnetic in a field and always experiences attraction.
- Electromagnet
- A coil of wire (solenoid) carrying a current, often around an iron core, producing a strong magnetic field that can be switched on and off.
- Like poles repel; unlike poles attract.
- A current-carrying wire creates a circular magnetic field around it.
- An electromagnet's strength increases with more turns, a bigger current, or an iron core.
Key formulas
Force on a conductor
F = B × I × L
force = magnetic flux density × current × length (Higher tier).
Required practicals
- Investigate how the strength of an electromagnet depends on the current or number of turns.
Worked example
State three ways to increase the strength of an electromagnet.
- 1Increase the current flowing through the coil.
- 2Increase the number of turns on the coil.
- 3Add an iron core inside the coil.
- 4Each change increases the magnetic flux density produced.
Answer: More current, more turns, and adding an iron core.
Common mistakes
✗ Drawing field lines from south to north.
✓ Field lines always go from north to south outside the magnet.
✗ Saying an induced magnet can repel.
✓ Induced magnetism always causes attraction.
✗ Confusing magnetic and electric fields.
✓ Magnetic fields act on magnetic materials and moving charges; electric fields act on all charges.
Quick check
Try these, then reveal the answers.
What happens when two north poles are brought together?Reveal answer
They repel.
Name one way to make an electromagnet stronger.Reveal answer
Increase the current, add more turns, or use an iron core.
In which direction do magnetic field lines point?Reveal answer
From north to south outside the magnet.
Exam tips
- Show field direction with arrows from north to south on every field diagram.
- For the required practical, change only one variable (current or turns) at a time.
- Use the phrase 'magnetic flux density' when describing field strength at Higher tier.
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Frequently asked questions
What is the difference between a permanent and an induced magnet?+
A permanent magnet always produces its own magnetic field; an induced magnet only becomes magnetic when placed in a field and then always experiences a force of attraction.
How can you increase the strength of an electromagnet?+
Increase the current, add more turns to the coil, or place an iron core inside the coil.
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