CBSE Class 12-science Answered

Consider the circuit as shown in figure 

Let a coil of a few turns is connected to a battery C and a sensitive galvanometer G through a two way key 1, 2, and 3.

When the North Pole of the magnet is moved towards the coil, the upper face of the coil acquires north polarity and hence repels the magnet. So, the work has to be done against the force of repulsion in bringing the magnet closer to the coil. Similarly, when the N pole of the magnet is moved away from the coil, the upper face develops south polarity. So, the work has to be done against the force of attraction in taking the magnet away from the coil.

Hence, this mechanical work done in moving the magnet w.r.t coil change into electrical energy producing induced current. Thus, the energy is transformed only. Hence, Lenz’s law obeys principle of conservation of energy.