Edexcel GCSE Combined Science CP12 and CP13 Magnetism and the motor effect: a complete overview of magnets, electromagnets and electromagnetic induction

What CP12 and CP13 actually demand

Magnetism and the motor effect, on Physics Paper 2, reward a clear understanding of magnetic fields, how an electromagnet is made and strengthened, and the rules for the size and direction of the motor-effect force. CP13 adds the idea of electromagnetic induction.

This guide walks through the topic and ties together the matching dot-point page, which has its own practice questions.

Magnets and magnetic fields

A permanent magnet is always magnetic; an induced magnet (iron) is only magnetic in a field. Like poles repel, unlike poles attract. A magnetic field runs from north to south outside the magnet and is strongest at the poles, where the field lines are closest.

Electromagnets and the motor effect

A current in a wire makes a circular field; a solenoid (coil) makes a strong field like a bar magnet, and with an iron core forms an electromagnet that can be switched and varied. The motor effect is the force on a current-carrying wire in a magnetic field; it grows with current or field strength and reverses if either is reversed.

Electromagnetic induction (CP13)

When a conductor and a magnetic field move relative to each other, or the field through a coil changes, a potential difference is induced. This is the basis of generators (which make electricity) and transformers (which change voltage).

How CP12 and CP13 are examined

• Magnets and fields. Distinguishing permanent and induced magnets and drawing field lines.
• Electromagnets. Explaining the solenoid and how to strengthen the field.
• Motor effect. Stating how to change the size and direction of the force.
• Induction. Recognising induction as the principle behind generators.

Check your knowledge

A mix of recall and application questions covering CP12 and CP13. Attempt them under timed conditions, then check against the solutions.

1. State the difference between a permanent and an induced magnet. (2 marks)
2. In which direction do magnetic field lines run outside a magnet? (1 mark)
3. Where is a magnetic field strongest? (1 mark)
4. What shape of magnetic field forms around a straight current-carrying wire? (1 mark)
5. How can you make an electromagnet stronger? (1 mark)
6. Name the effect that produces a force on a current-carrying wire in a field. (1 mark)
7. State two ways to increase the motor-effect force. (2 marks)
8. What is induced when a magnetic field through a coil changes? (1 mark)