. F ARADAY ’ S L AW OF I NDUCTION From the experimental observations, Faraday arrived at a conclusion that an emf is induced in a coil when magnetic flux through the coil changes with time. Experimental observations discussed in Section . can be explained using this concept.
The motion of a magnet towards or away from coil C in Experiment . and moving a current-carrying coil C towards or away from coil C in Experiment . , change the magnetic flux associated with coil C . The change in magnetic flux induces emf in coil C .
It was this induced emf which caused electric current to flow in coil C and through the galvanometer. A plausible explanation for the observations of Experiment . is as follows: When the tapping key K is pressed, the current in coil C (and the resulting magnetic field) rises from zero to a maximum value in a short time. Consequently, the magnetic flux through the neighbouring coil C also increases.
It is the change in magnetic flux through coil C that produces an induced emf in coil C . When the key is held pressed, current in coil C is constant. Therefore, there is no change in the magnetic flux through coil C and the current in coil C drops to zero. When the key is released, the current in C and the resulting magnetic field decreases from the maximum value to zero in a short time.
This results in a decrease in magnetic flux through coil C and hence again induces an electric current in coil C * . The common point in all these observations is that the time rate of change of magnetic flux through a circuit induces emf in it. Faraday stated experimental observations in the form of a law called Faraday’s law of electromagnetic induction . The law is stated below.
FIGURE . A plane of surface area A placed in a uniform magnetic field B . FIGURE . Magnetic field B i