The Discovery That Lights the World
🧲 The Discovery That Lights the World
In 1831, Michael Faraday pushed a bar magnet into a coil of wire — and a current flowed. He pulled it out — and a current flowed in the opposite direction. He held the magnet still — nothing. This seemingly simple observation is the foundation of almost all electricity generation on Earth. Every wind turbine, every hydroelectric dam, every coal and gas and nuclear power station uses this exact principle — a magnetic field changing near a conductor causes a current to flow. Without electromagnetic induction, there would be no mains electricity, no dynamos, no transformers, and no modern civilization as we know it. Faraday's coil experiment is one of the most consequential moments in the history of science.
Inside an AC generator — click each component to see how electromagnetic induction produces alternating current.
- 1Permanent magnets —
- 2Rotating coil —
- 3Slip rings —
- 4AC output —
Figure 1: Inside an AC generator — click each component to see how electromagnetic induction produces alternating current.
Electromagnetic induction is the process by which a changing magnetic field induces (creates) a potential difference (voltage) in a conductor, which drives a current if the circuit is complete.
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🧠 Memory Aids
Faraday's key insight: "Move it, change it, generate it." The field must CHANGE near the conductor to induce a current. Still = nothing. Moving = current.
Generator vs motor:
- Generator: you give it spin, it gives you electricity (G = give spin → get electricity)
- Motor: you give it electricity, it gives you spin (M = money in → movement out)
Lenz's law — "nature is lazy and opposes change": The induced current always makes life harder for whatever is causing it. Push a magnet in — current pushes back. This is nature "resisting" change to conserve energy.
Ways to increase induced EMF — FAST:
- Faster movement
- Area of coil larger
- Stronger magnet
- Turns of coil more
Quick Check: List three ways to increase the induced EMF in a generator.
Any three from: (1) Rotate the coil faster / move the magnet faster. (2) Use a stronger magnet. (3) Increase the number of turns in the coil. (4) Increase the area of the coil.
Now try it yourself
This topic in real past papers
Every real exam question we've found on electromagnetic induction, with a full worked answer.