Question

State Lenz's law of electromagnetic induction.

Answer 1

Lenz's law states that when an emf is generated by a change in magnetic flux according to Faraday's Law, the polarity of the induced emf is such, that it produces a current whose magnetic field opposes the change which produces it.
Mathematically,

( : Emf ; N : Number of turns ; : Magnetic Flux)
Here the negative sign is due to the Lenz's law.