Magnetism and electromagnetism — AQA GCSE Physics

Magnetism and electromagnetism is a core topic in AQA GCSE Physics that explores the fundamental principles of magnetic fields, electromagnets, and the motor effect. You'll learn how permanent magnets and induced magnets behave, how to plot magnetic field patterns, and how electricity can create magnetism. This topic is essential for understanding how electric motors, loudspeakers, and generators work – technologies that are central to modern life.

The topic builds on your knowledge of electric circuits and forces. You'll discover that a current-carrying wire experiences a force in a magnetic field (the motor effect), which is the basis for electric motors. You'll also learn about electromagnetic induction – how a changing magnetic field can induce a potential difference – which is how generators and dynamos produce electricity. These concepts are not only exam favourites but also explain how renewable energy sources like wind turbines generate power.

Mastering this topic requires you to visualise magnetic fields in 3D and apply Fleming's left-hand rule. You'll need to recall specific experiments, such as plotting compasses around a bar magnet or using a current balance. The topic also links to 'Forces' and 'Energy' – for example, the force on a conductor depends on current, magnetic flux density, and length, and the induced potential difference can be calculated using Faraday's law. By the end, you should be able to explain how a simple motor or generator works and calculate the size and direction of forces.

• →Magnetic fields: region around a magnet where a force acts on another magnet or magnetic material. Field lines go from north to south outside the magnet.
• →Electromagnetism: a current-carrying wire produces a circular magnetic field around it. The right-hand grip rule gives the direction.
• →Motor effect: a current-carrying conductor placed in a magnetic field experiences a force. Use Fleming's left-hand rule to find direction: thumb = force, first finger = field, second finger = current.
• →Electromagnetic induction: a potential difference is induced across a conductor when it cuts magnetic field lines. The size depends on the rate of change of flux, number of turns, and magnetic flux density.
• →Transformers: use electromagnetic induction to change voltage. For an ideal transformer, Vp/Vs = Np/Ns and power in = power out (VpIp = VsIs).

• Poles are the regions where magnetic forces are strongest.
• Like poles repel; unlike poles attract.
• Attraction and repulsion between poles are non-contact forces.
• Permanent magnets produce their own magnetic field.
• Induced magnets become magnetic when placed in a magnetic field.
• Induced magnetism always causes a force of attraction.
• Induced magnets lose most or all of their magnetism quickly when removed from a magnetic field.

• 💡Remember that induced magnetism only results in attraction, never repulsion.
• 💡Be prepared to describe the difference between permanent and induced magnets clearly.
• 💡Ensure you can identify the poles of a magnet in a diagram.
• 💡Always draw field lines with arrows from north to south. In exam questions, you may be asked to plot the field around a bar magnet or a solenoid – make sure the lines are smooth and evenly spaced, and include at least three lines.
• 💡For motor effect calculations, use F = BIL (force = magnetic flux density × current × length). Remember that the length is the part of the conductor inside the magnetic field. If the wire is at an angle, use F = BIL sinθ.
• 💡When explaining electromagnetic induction, mention 'cutting field lines' or 'changing magnetic flux'. For a generator, describe how the coil rotates, causing the induced potential difference to alternate. Use the right-hand dynamo rule for direction of induced current.

• Confusing permanent magnets with induced magnets.
• Assuming induced magnetism can cause repulsion (it only causes attraction).
• Failing to identify that magnetic force is a non-contact force.
• Misconception: Magnetic field lines are real and can be seen. Correction: Field lines are a model to show the direction and strength of the field; they are not physical lines. The closer the lines, the stronger the field.
• Misconception: The force on a current-carrying wire is always perpendicular to the wire. Correction: The force is perpendicular to both the current and the magnetic field direction (Fleming's left-hand rule). If the wire is parallel to the field, there is no force.
• Misconception: Transformers work with DC. Correction: Transformers require a changing magnetic field, so they only work with alternating current (AC). DC would produce a constant field and no induction.