What is Electromagnetic Induction?
Electricity and magnetism are deeply connected — one of the greatest discoveries in physics is that a changing magnetic field can create an electric current. This phenomenon is called electromagnetic induction, and it was discovered experimentally by Michael Faraday in 1831.
Before Faraday, scientists already knew that an electric current produces a magnetic field (Oersted, 1820). Faraday asked the reverse question: can a magnetic field produce an electric current? After years of experiments, he found the answer — but with a crucial twist.
The process by which a changing magnetic field through a conductor creates (induces) an electromotive force (EMF) and, if the circuit is complete, an electric current.
The key word is changing. A static (stationary) magnet sitting inside a coil does nothing. It is only when there is relative motion between the magnet and the coil — or when the magnetic field through the coil is changing — that a current is induced.
Think of it like pushing a door. A door just sitting there doesn't move. You have to push (change the situation) to make something happen. Similarly, a magnet just sitting near a wire does nothing — you have to move it (change the magnetic field) to induce a current.
Faraday's Key Experiments
Michael Faraday performed a series of elegant experiments to understand electromagnetic induction. Here are the three most important setups:
Experiment 1: Moving a magnet into a coil
Faraday connected a coil of wire to a galvanometer (a sensitive current detector). When he pushed a bar magnet into the coil, the galvanometer needle deflected — a current was flowing! When he stopped moving the magnet, the current dropped to zero. When he pulled the magnet out, the current flowed in the opposite direction.
Experiment 2: Moving the coil instead
Faraday found that it didn't matter whether he moved the magnet or the coil — as long as there was relative motion between them, a current was induced. This confirmed that what matters is the change in magnetic field experienced by the coil.
Experiment 3: Two coils (mutual induction)
Faraday wrapped two coils around an iron ring. When he switched the current on or off in the first coil (the primary), a brief current appeared in the second coil (the secondary). The changing current in the primary created a changing magnetic field, which induced a current in the secondary.
The galvanometer is central to these experiments. It detects very small currents and shows their direction by deflecting left or right. A deflection means current is flowing; no deflection means no current.
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