Unit Opener

This unit covers two closely linked topics printed together as one combined Tamil Nadu Samacheer Kalvi unit: electromagnetic induction (how a changing magnetic flux produces an emf) and alternating current (how the resulting sinusoidal emf behaves once it drives a real circuit). The unit opens with Faraday's own words -- 'Nature is our kindest friend and best critic in experimental science if we only allow her intimations to fall unbiased on our minds' -- a reminder that the whole subject grew out of careful, patient experimentation rather than pure theory.

The unit's learning objectives, stated up front, are: the phenomenon of electromagnetic induction itself; applying Lenz's law to find the direction of an induced emf; the concept of eddy currents and their practical uses; the phenomena of self-induction and mutual induction; the various physical methods of producing an induced emf; the construction and working of AC generators; the principle of transformers and their role in long-distance power transmission; the notion of the root-mean-square value of an alternating current; the idea of phasors and phase relationships in different AC circuits; power in an AC circuit and wattless current; and the conservation of energy during LC oscillations. These objectives map directly onto the unit's nine numbered sections (4.1 through 4.9), each of which builds on the ideas developed in the sections before it.