L.2 Magnetism & Electromagnetism
Exploring magnetic fields, electromagnets, the motor effect, and electromagnetic induction.
Questions to explore
- ? How can electricity create magnetism — and magnetism create electricity?
- ? What physics spins every motor and lights every generator on Earth?
💡 Key ideas, explained simply
🧲 Making magnetism from electricity
A current in a wire creates a magnetic field around it. Coil the wire into a solenoid and add an iron core and you have an electromagnet — a magnet you can switch on and off.
Strengthen it three ways: more current, more turns of wire, or a soft-iron core.
🔁 The motor effect and induction
Put a current-carrying wire in a magnetic field and it feels a force — the *motor effect* — which spins every electric motor. Use Fleming's left-hand rule for the direction.
Run it backwards: move a magnet near a coil and you *induce* a voltage. That is electromagnetic induction, the principle behind every generator.
📖 Key terms
- Magnetic field
- The region where a magnet or current exerts a force; shown by field lines N→S.
- Electromagnet
- A solenoid with a current and iron core — a switchable magnet.
- Solenoid
- A coil of wire that behaves like a bar magnet when current flows.
- Motor effect
- The force on a current-carrying wire in a magnetic field.
- Electromagnetic induction
- Generating a voltage by changing the magnetic field near a coil.
- Fleming's left-hand rule
- Thumb = motion, first finger = field, second finger = current.
✏️ Worked example
Strengthening an electromagnet
An electromagnet is too weak to lift a steel bar. Suggest three changes that would make it stronger.
- 1
Increase the current
A bigger current makes a stronger magnetic field.
- 2
Add more turns
More coils of wire concentrate more field lines.
- 3
Add a soft-iron core
Iron greatly boosts the field and drops away when switched off.
Any of these raises the magnetic field strength — scrapyard cranes use all three.
🚉 Physics around you
Maglev trains float on electromagnets and are pushed along with no wheels touching the track — almost frictionless, and record-breakingly fast. The same induction that runs generators also charges your phone wirelessly.
🎯 Nail it in the exam
Magnetic Fields and Electromagnets
Magnetic field lines go from north to south outside a magnet. Arrows show direction. Closer lines = stronger field.
Electromagnet: a solenoid (coil of wire) with a current; strength increased by adding an iron core, increasing current, or adding more turns. Past papers often ask for ways to increase the strength and applications like electric bells, relays, and loudspeakers.
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Draw field lines that never cross.
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To remember the right‑hand grip rule for a solenoid: fingers curl in the direction of current, thumb points to the N pole.
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In ‘suggest’ questions, always link increased magnetic field to a clear outcome (e.g., ‘stronger electromagnet can lift heavier objects’).
Motor Effect and Induction
When a current‑carrying wire is placed in a magnetic field, it experiences a force (the motor effect). Direction given by Fleming’s left‑hand rule: thuMb = Motion, First finger = Field, seCond finger = Current.
Electromagnetic induction: when a magnet is moved into a coil, a voltage is induced. The induced voltage increases if the magnet moves faster, the coil has more turns, or the magnet is stronger. This is the basis of generators and transformers.
Past paper questions often show a diagram of a loudspeaker or a simple motor and ask you to explain how it works using the motor effect.
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Force on the wire is maximum when the wire is perpendicular to the field; zero when parallel.
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For induction, always mention ‘change in magnetic field’ – if the magnet is stationary, no voltage is induced.
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Transformers only work with AC because a changing magnetic field is required.
🧠 Check your understanding
Tap an answer to see if you're right — and why.
Q1. Which of the following will increase the strength of an electromagnet?
Q2. What rule is used to determine the direction of the force on a current‑carrying conductor in a magnetic field?
📝 Exam-style questions
Try each one, then reveal the model answer.