Electromagnetism

Objective: Relate changing magnetic flux to an induced potential difference.

Faraday’s law states that a changing magnetic flux through a conducting loop induces an electromotive force; in an introductory model, the magnitude increases with faster flux change and more turns. Flux can change by moving a magnet, moving a coil, changing field strength, or changing orientation. A stationary magnet and stationary loop with constant flux produce no sustained induced voltage from this mechanism. Lenz’s law describes induced-current direction as opposing the change that produced it, consistent with energy conservation. Induction does not guarantee current unless a conducting path is closed. An induced emf is a voltage-like energy-per-charge quantity, not energy created from nothing.

Objective: Apply electromagnetism to calculations, evidence, and specified situations.

A changing magnetic flux linkage induces emf. For N turns, average magnitude is N|ΔΦ|/Δt; flux is BAcosθ for a uniform field, with θ measured from the surface normal. Lenz’s law gives the induced response that opposes the change in flux, consistent with energy conservation. A constant flux through a stationary loop gives no induced emf in this model. An ideal transformer’s voltage ratio equals its turns ratio and assumes time-varying flux, negligible losses, and suitable coupling.