Question

Lenz's law follows the law of conservation of energy. Explain.

Hint:

Remember the core idea: "There's no such thing as a free lunch." You can't get electrical energy for free. Lenz's law ensures that you must do work (provide energy) to generate induced current.

Answer 1

Step 1: Understanding the Concept:
Lenz's law states that the direction of the induced electromotive force (e.m.f.) and hence the induced current in a closed circuit is such that it opposes the change in magnetic flux that produced it. This principle is directly linked to the law of conservation of energy.
Step 2: Detailed Explanation:
Let's consider an example: moving the north pole of a bar magnet towards a closed coil.
1. As the north pole approaches the coil, the magnetic flux through the coil increases.
2. According to Lenz's law, an e.m.f. and current will be induced in the coil in a direction that opposes this increase in flux. To oppose the approaching north pole, the face of the coil towards the magnet must become a north pole itself (like poles repel).
3. This induced north pole creates a repulsive force on the approaching magnet. To keep the magnet moving towards the coil, we must do mechanical work against this repulsive force.
4. This mechanical work done by the external agent is converted into electrical energy in the coil, which manifests as the induced current and can dissipate as heat (\(I^2R\)).
What if Lenz's Law was violated?
Suppose the induced current supported the change instead of opposing it. In our example, the coil would form a south pole. This south pole would attract the approaching north pole, pulling it in faster. This would induce an even larger current, creating a stronger attraction, and so on. This would lead to a self-sustaining increase in kinetic and electrical energy without any external work being done, which would be a clear violation of the law of conservation of energy.
Step 3: Final Answer:
Thus, the very opposition described by Lenz's law necessitates the input of energy (usually mechanical) to produce electrical energy, thereby upholding the principle of conservation of energy.