Production of Induced EMF And Current
In Fig. is shown an insulated coil whose terminals are connected to a sensitive galvanometer
G. It is placed close to a stationary bar magnet initially at position AB (shown dotted). As seen, some
flux from the N-pole of the magnet is linked with or threads through the coil but, as yet, there is no
deflection of the galvanometer. Now, suppose that the magnet is suddenly brought closer to the coil in
position CD (see figure). Then, it is found that there is a jerk or a sudden but a momentary deflection
in the galvanometer and that this lasts so long as the magnet is in motion relative to the coil, not
otherwise. The deflection is reduced to zero when the magnet becomes again stationary at its new
position CD. It should be noted that due to the approach of the magnet, flux linked with the coil is
increased.
In Fig. is shown an insulated coil whose terminals are connected to a sensitive galvanometer
G. It is placed close to a stationary bar magnet initially at position AB (shown dotted). As seen, some
flux from the N-pole of the magnet is linked with or threads through the coil but, as yet, there is no
deflection of the galvanometer. Now, suppose that the magnet is suddenly brought closer to the coil in
position CD (see figure). Then, it is found that there is a jerk or a sudden but a momentary deflection
in the galvanometer and that this lasts so long as the magnet is in motion relative to the coil, not
otherwise. The deflection is reduced to zero when the magnet becomes again stationary at its new
position CD. It should be noted that due to the approach of the magnet, flux linked with the coil is
increased.
Next, the magnet is suddenly withdrawn away from the coil as in Fig. 7.2. It is found that again
there is a momentary deflection in the galvanometer and it persists so long as the magnet is in
motion, not when it becomes stationary. It is important to note that this deflection is in a direction
opposite to that of Fig. 7.1. Obviously, due to the withdrawal of the magnet, flux linked with the coil
is decreased.
The deflection of the galvanometer indicates the production of e.m.f. in the coil. The only cause
of the production can be the sudden approach or withdrawal of the magnet from the coil. It is found
that the actual cause of this e.m.f. is the change of flux linking with the coil. This e.m.f. exists so long
as the change in flux exists. Stationary flux, however strong, will never induce any e.m.f. in a stationary conductor. In fact, the same results can be obtained by keeping the bar magnet stationary and
moving the coil suddenly away or towards the magnet.
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