Question

why is lenz law a consequence of the law of conservation of energy

Answer 1

Lenz law is in accordance with the law of conservation of energy. See induced EMF produces a current that opposes the change in flux, because a change in flux means a change inenergy. Energy can enter or leave, but not instantaneously. Lenz' law is a consequence.

Answer 2

As in the lenz law the direction of the induced EMF or current always tends to oppose the very cause which produces the current so it is a consequence of the law of conservation of mass