Why does a changing magnetic flux induce an EMF in "opposite direction"? Faraday's Law of Induction tells us that a changing magnetic flux induces an EMF in the conductor, causing an electric current to flow.
By Lenz's Law, we get the direction of induced EMF which turns out to be in the opposite direction of the changing magnetic flux. But why is it in the opposite direction ? What would happen if it would have been in the same direction ?
 A: Besides the answer "because that's how the maths works", there is a conservation of energy argument.
Consider a dipole magnet, which you drop through a metal tube. As it falls, it creates a changing magnetic field, and that induces a current in the tube to oppose the changing magnetic field.
What do you observe? You find that the magnet slows down as it falls through the tube. Its kinetic energy, picked up from falling through the tube, is converted into electrical current.
This is needed for energy to be conserved. If it went in the same direction, then the magnet would instead speed up. If this were the case, you could potentially loop the magnet through the metal tube again and again and create a perpetual motion machine.
So in short: if it went in the same direction, energy would not be conserved. Lenz's law ensures energy is conserved.
A: Actually the Lenz law is connected to energy conservation (one of the most fundamental "law" of nature).
So let us suppose you have a fixed conducting loop and a movable magnet. If you move the magnet towards the loop and suppose the induced current was the other way round then the loop will attract the magnet and so with just a little bit of your energy input to the system you could have made a large amount energy out of it. But surely that can't happen. You can't create energy.
"So ultimately nature keeps its energy-safe locked".
