CHAPTER 25 : ELECTRO - MAGNETIC INDUCTION
When Oersted established that electric current produces a magnetic field i.e., a varying electric
field produces a magnetic field, an obvious question arises: "can a varying magnetic field produce
electric current?" Faraday found the answer to be in the affirmative.
25.1 Faraday's Experiments
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The experiments are performed using a bar magnet, a coil and a galvanometer. There were a number
of observations made. One was that whenever the magnet was set in motion ( indicated by the arrow)
relative to the coil, current was found to flow through the coil. The direction of current induced in the
coil was found to depend on the pole of the magnet facing the coil and on the direction of the motion of
the magnet. It can be seen from fig: 1 that the induced current flowing through the coil is always such that it
opposes the motion of the magnet. This process of producing induced current due to a varying
magnetic field is called electro- magnetic
Now, the intensity on the axis of a bar magnet decreases with increase in distance from the magnet
and vice versa. The moving magnet therefore brings about change in the magnetic flux through the coil.
The induced current or induced e. m. f. must be correlated with the charge in the magnetic flux.