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Question
Show that Lenz's law is a consequence of conservation of energy.
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Solution
According to Lenz law, the polarity of the induced emf is such that it opposes the change in magnetic flux responsible for its production.
Experiment:
When the bar magnet with its N-pole is moved towards the coil, the induced current produced in coil S opposes the motion of magnet. It will happen so, if the induced current in the coil S produces magnetic field lines from left to right i.e., if the induced current flows through the coil S in clockwise direction (when seen from left).
Lenz Law and Principle of Conservation of Energy
Lenz law is in accordance with the law of conservation of energy. In the above experiment, when N-pole of magnet is moved towards the coil, the right face of the coil acquires North polarity. Thus, work has to be done against the force of repulsion in bringing the magnet closer to the coil.
When N pole of magnet is moved away, South pole develops on the right face of the coil. Therefore, work has to be done against the force of attraction in taking the magnet away from the coil.
This mechanical work in moving the magnet with respect to the coil changes into electrical energy producing induced current. Hence, energy transformation takes place. Hence, we can say that Lenz's law is a consequence of conservation of energy.
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