Question

Lenz’s law is a consequence of the law of conservation of
A. Energy only
B. Charge only
C. Momentum only
D. Energy and momentum

Answer 1

Hint: Lenz’s law states that the current induced in a circuit is directed such that the magnetic field produced by the circuit opposes the change in the magnetic field.

Complete step-by-step answer:
We need to understand Lenz's Law first. Lenz’s law says that,

“The current induced in a circuit due to a changing magnetic field is directed to oppose the change in flux and to exert a mechanical force which opposes the motion”

Mathematically, we can write,
$\varepsilon =-\dfrac{\partial {{\phi }_{B}}}{\partial t}$

Where,
$\varepsilon $ is the electromotive force generated in the circuit
${{\phi }_{B}}$ is the change in magnetic flux.

The negative sign suggests that the induced electromotive force opposes the change in the magnetic field.

So, we can see the phenomenon in this manner:

If you move a current loop through a magnetic field, the metallic loop has a specific amount of kinetic energy. Moving the wire produces some amount of force on the free electrons inside the wire. As a result, an electromotive force is generated.

Now, electrical energy has to be generated from somewhere. Due to conservation of energy, we can say that the total energy of the system has to be constant. Now, the two potential sources of energy in this system are,

Total Energy = Kinetic Energy + Electrical Energy

At first, there was only Kinetic energy of the metallic loop. Now, if the electrical energy has increased by some amount, the kinetic energy of the wire must decrease to compensate for the increase in electrical energy.

That is why the current induced must oppose the motion of the wire or the change in the magnetic field.
It is the statement of Lenz’s law.
Hence, the correct option is, (A).

Note:
We can find the magnitude of the electromotive force in a current loop using Faraday’s Law. However, we need to depend on Lenz’s law to identify the direction of that force. If the flux is increasing, the induced field must decrease this increase.