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On the syllabus: GCSE PhysicsA-Level Physics
Every time you charge your phone wirelessly, electricity is being created from nothing but a changing magnetic field — no battery-to-battery contact, no wires connecting charger to phone. How is it possible to push electrons through a circuit inside your phone using only a magnetic field outside it?
Every time you charge your phone wirelessly, electricity is being created from nothing but a changing magnetic field — no battery-to-battery contact, no wires connecting charger to phone. How is it possible to push electrons through a circuit inside your phone using only a magnetic field outside it?
Michael Faraday discovered in 1831 that a changing magnetic field induces a voltage. This single insight — that motion creates electricity — is the operating principle of every power station on Earth. Whether the source is a coal furnace, a nuclear reactor, or a wind turbine, the final step is always the same: spin a magnet near coils of wire.
A changing magnetic flux through a coil induces an EMF (voltage). The induced EMF opposes the change that caused it — this is Lenz's Law. The faster the flux changes, or the more turns in the coil, the greater the induced EMF.
Lenz's Law is conservation of energy in disguise. If the induced current helped the flux change instead of opposing it, you'd get a self-accelerating system — free energy. Instead, moving a magnet into a coil induces a current that creates its own opposing magnetic field, making you do work to push the magnet in. That work is exactly the electrical energy generated. Transformers, generators, induction cooktops, wireless chargers, and metal detectors all operate on electromagnetic induction.