Electromagnetic Induction — A/L Physics

Magnetic Flux (Φ) The product of the magnetic flux density and the area perpendicular to the field. Magnetic flux measures the total magnetic field passing through a given area. It is defined as Φ = BA cosθ, where θ is the angle between the field direction and the normal to the area. The unit is the weber (Wb). For example, a loop of area 0.1 m² placed perpendicular to a 0.5 T field has a flux of 0.05 Wb.

Faraday’s Law of Induction The magnitude of the induced emf is equal to the rate of change of magnetic flux linkage. Mathematically, ε = –N(dΦ/dt), where N is the number of turns. The negative sign indicates Lenz’s law. A practical example: moving a magnet quickly into a coil induces a larger emf than moving it slowly, because the flux changes faster.

Lenz’s Law The direction of the induced current is such that it opposes the change causing it. This is a consequence of energy conservation. If you push a magnet into a coil, the induced current creates a magnetic field that repels the magnet, requiring you to do work. This explains why generators require mechanical input power.