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e.m.f. When the bar magnet is near the coil, some of the magnetic lines of force are passing through the coil; that is 'some magnetic flux is linked with the coil'. Now when there is relative motion between the coil and the magnet, the amount of flux linked with the coil is changing. When the relative motion stops, there is no further change in the amount of the flux linked. So we conclude that, "when there is a change in the flux linked with the coil, there is an emf generated in the coil." The observation that a faster motion of the magnet gives rise to a larger deflection shows that the emf generated depends upon the rate of change of the flux linking the coil. The current resulting from this "induced emf." is called the induced current". When a Current flows in a coil, magnetic flux is produced due to this current and the coil now acts as a magnet. Which face of the coil acts like a north pole and which face becomes a south pole depends upon the direction of the current in the coil. Thus, we see that the direction of the induced current and the corresponding direction of the resulting magnetic field is a consequence of the conservation of energy. This leads us to Lenz's law which states: “If an agency generates an induced emf through its action (such as motion of the magnet as illustrated) the induced emf would be such that the current produced by this emf would generate a magnetic field such as to oppose the action of the agency." 3. Faraday's Law Faraday gave the law relating the induced emf in a circuit with the rate of change of the flux. 4. Self-induction We have learnt that when a current passes through a coil, some magnetic field is created so that the coil itself behaves like a magnet. The magnetic flux produced by the current in the coil is linked with the coil itself and when the curent in the coil changes, this flux linked with the coil also changes. Under such circumstances also, there would be an emf induced in the coil which is called the 'self-induction' The value of mutual inductance of a system of two coils depends upon their shapes, sizes, their number of turns, distance between them, their mutual inclination angle and the
material on which they are wound. 49. (a) Text-book of Physics (Part - II), op.cit, p. 94
"Electromagnetic waves discovered relatively recently-only in
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