SUMMARY

This chapter's own bullet-point summary condenses every major law and definition of the unit into one line each. Whenever the magnetic flux linked with a closed coil changes, an emf is induced and hence an electric current flows -- this is electromagnetic induction. Faraday's first law: whenever magnetic flux linked with a closed circuit changes, an emf is induced. Faraday's second law: the induced emf's magnitude equals the time rate of change of the linked flux. Lenz's law: the induced current's direction always opposes the cause producing it, and this law is itself established on the basis of energy conservation. Fleming's right hand rule: with the index finger along the field and the thumb along the conductor's motion, the middle finger gives the induced current's direction.

Even for a sheet or plate conductor, an emf is induced when its linked flux changes, and the resulting currents -- flowing in concentric circular paths with no definite wire path to follow -- are eddy (or Foucault) currents. An inductor stores energy in a magnetic field when current flows through it. If the flux linked with a coil changes (because of its OWN changing current), an emf is induced in that same coil -- self-induction, giving the self-induced emf. If a coil's current changes and induces an emf in a NEIGHBOURING coil, that is mutual induction, giving the mutually induced emf.

An AC generator (alternator) converts the mechanical energy used to rotate a coil or field magnet into electrical energy; some generators carry three separate coils giving three separate emfs, called three-phase AC generators. A transformer is a stationary device that transforms AC electrical power from one circuit to another without changing frequency; its efficiency is the ratio of useful output power to input power. An alternating voltage changes polarity at regular intervals, with the resulting current changing direction correspondingly. The average value of AC is the average of its values over a positive (or negative) half-cycle; the RMS (or effective) value is the square root of the mean of the squares of all its values over one full cycle. …