Lenz’s law is a consequence of the law of conservation of which of the following?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Energy
By Lenz’s law, the induced emf has a polarity that tends to drive a current opposing the change in magnetic flux that produced it.
Option (1) Momentum — Incorrect. The direction of the induced current comes from an energy balance. The work done against the opposing force equals the heat produced. Momentum plays no part in this argument.
Option (2) Energy — Correct. The opposition makes the energy account balance:
When a magnet is pushed towards a coil, the induced current repels it. So a person must do work to move the magnet. This work appears as the Joule heat of the induced current.
If the current flowed the other way, it would attract the magnet. The magnet would then speed up with no energy spent. Such a perpetual-motion machine violates the law of conservation of energy.
Option (3) Charge — Incorrect. Conservation of charge decides how currents divide at a junction; it says nothing about the direction in which an induced current flows.
Option (4) Current — Incorrect. There is no law of conservation of current; the induced current is the quantity whose direction Lenz’s law gives.
NCERT (2026-27):
Lenz’s Law and Conservation of Energy – “A little reflection on this matter should convince us on the correctness of Lenz’s law. … If this can happen, one could construct a perpetual-motion machine by a suitable arrangement. This violates the law of conservation of energy and hence can not happen.”
Lenz’s Law and Conservation of Energy – “… In this situation, the bar magnet experiences a repulsive force due to the induced current. Therefore, a person has to do work in moving the magnet. … This energy is dissipated by Joule heating produced by the induced current.”