If I move a magnet towards the coil then the magnet will experience a restive force because of Lenz's law. This way mechanical energy will convert into electrical energy.
But what if the magnet and the coil are a sufficiently large distance apart? The change in the magnetic field travels at the speed of light so the magnet will not feel any restive force instantly. Doesn't this violate the energy conservation law? Because we fix the magnet to a particular point before the restive force arrives at the magnet. And we will able to produce arbitrarily large energy in the coil.
If the magnet starts to move at time t=t1 and lets assume that t0 is the time taken for the flux linking the coil to change due to motion of the magnet.
t0 = (distance between the magnet and the coil/velocity of light)
the magnet will begin to experience resistance at time (t1+2t0). so the delay will be 2t0. In this time period (2t0), magnet is free without experiencing any resisting force. During this time period we can draw current arbitrarily large value by making arbitrarily large numbers of turns of the coil. If energy is conserved, then what mechanism stops us to draw any large amount of power from the coil ?