Physics · Electromagnetic Induction · NEET
When you push a magnet into a coil, the induced current makes the coil act like a magnet that pushes back. You must do work against this push. That work does not vanish — it turns into the electrical energy of the induced current (and heat in the wire). So the 'opposing' behaviour is exactly what makes energy balance: work you put in = electrical energy you get out. Lenz's law is just energy conservation written for induction.
Then the coil would pull the incoming magnet in faster. The magnet speeds up on its own, flux changes faster, current grows, which pulls even harder. You would get more and more kinetic energy AND more and more electrical energy, all from nothing. That is a perpetual motion machine. Since energy cannot be created from nothing, the induced current MUST oppose the motion. That is why Lenz's law has no exceptions.
From the mechanical work done by whoever (or whatever) moves the magnet or coil. In a generator, the turbine does this work. The magnetic field does not supply the energy — it only redirects the work you do into electrical form. Formula view: power you put in as force times velocity (P = Fv) equals the electrical power generated (P = EI, that is emf times current).
Yes. Faraday's law is emf = -N dPhi/dt. The minus sign is Lenz's law in math form. It says the induced emf is directed to oppose the change in flux. So the minus sign is the fingerprint of energy conservation inside the equation.
Yes. The electrical energy produced is dissipated as heat in the resistance of the coil (I squared R). If the coil had zero resistance the current would keep circulating, but in real coils the work you do ends up mostly as heat. Either way, the mechanical work in equals the electrical/heat energy out — nothing is lost or gained.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is not a fully separate law. Faraday's law gives the size of the induced emf; Lenz's law (the minus sign) gives its direction. Together they describe induction, and the direction rule exists to keep energy conserved.
No. Violating it would mean creating energy from nothing, which breaks conservation of energy. That is why NEET treats Lenz's law as absolute — it is backed by one of physics' strongest laws.
Set mechanical power equal to electrical power: F times v = emf times I. For a rod of length l moving at speed v in field B, emf = Bvl, so the power you supply, F times v, equals Bvl times I, and that equals I squared R. This lets you find force, current, or heat quickly.
No. If nothing changes, the flux is constant, so dPhi/dt = 0 and there is no induced current. Energy is only needed while the flux is changing, because only then are you doing work against an opposing force.
NEET often asks 'which direction' and 'where does the energy come from' style questions, and sometimes numericals linking force, power and heat in a moving rod. Understanding that Lenz's law equals energy conservation lets you reason out the answer instead of memorising each case.
