Physics A2 · Magnetic fields. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Magnetic flux measures how much field passes through an area. It is the flux density multiplied by the area at right angles to the field. For a coil of N turns, the flux linkage is N times the flux through one turn.
An e.m.f. is induced whenever the flux linkage of a circuit changes: when a magnet moves near a coil, a coil turns, or the field changes. A steady flux, however large, induces nothing.
Faraday's law gives the size of the e.m.f. Lenz's law gives its direction: the induced current always acts to oppose the change that causes it. This follows from conservation of energy.
An e.m.f. needs a CHANGE in flux linkage. A magnet at rest inside a coil, or a magnet and coil moving together, give zero e.m.f. Check also whether a given angle is to the plane of the coil or to its normal.
Answer: 0.30 V
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