Faraday’s Law of Induction

Formula

Description

Faraday’s law states that a changing magnetic flux through a coil induces an electromotive force proportional to the number of turns and the rate of change of flux. The minus sign (Lenz’s law) says the induced EMF opposes the change that produced it. This is the principle behind transformers, generators, inductors, induction sensors, and wireless power.

Variables

• emf — Induced electromotive force (V)
• N — Number of turns
• ΔΦ — Change in magnetic flux (Wb)
• Δt — Time over which the change occurs (s)

Practical Notes

Faster flux changes or more turns give higher induced voltage—this is why ignition coils and flyback transformers use many turns and fast current interruption to generate high voltages.