Faraday's Induction
A moving magnet, a flowing current
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Summary
If a magnet near a coil moves, an electric current flows through the coil. When the magnet stops, the current stops. This is the heart of Faraday's law: a changing magnetic flux produces electricity.
In depth
In 1831 Michael Faraday made a simple observation: when he pushed a magnet into a coil and pulled it out again, the needle of a galvanometer deflected. When the magnet stopped, the needle returned to zero. The faster the motion, the bigger the deflection, and when the direction changed, so did the deflection. This observation gave rise to the law of electromagnetic induction: if the magnetic flux Φ through a circuit changes, an EMF (electromotive force) is induced in the circuit, with size ε = −dΦ/dt. The minus sign is Lenz's law: the induced current always flows in the direction that opposes the change in flux that produced it. This simple law is the foundation of today's electrical world: generators, transformers, induction hobs, dynamos and wireless charging pads are all built on it.
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