Physics · Electromagnetic Induction · NEET
Only the direction (the polarity). Lenz's law tells you WHICH WAY the induced current flows. The SIZE of the emf still comes from Faraday's law, emf = N x (dPhi/dt), and the current is I = emf/R. So use Faraday's law for 'how much' and Lenz's law for 'which way'.
Use 4 steps. Step 1: find the flux direction through the coil (where does B point). Step 2: is that flux increasing or decreasing? (magnet coming closer = increasing, going away = decreasing). Step 3: the induced current opposes the change, so if flux is increasing the induced current makes a magnetic field OPPOSITE to B; if decreasing it makes a field in the SAME direction as B to support it. Step 4: use the right-hand grip rule (curl fingers along current, thumb points to the induced field's North) to read the actual current direction in the wire.
The coil opposes the approach, so the face nearest the magnet becomes the SAME pole as the incoming pole. If the North pole approaches, the near face becomes North (like repels like) to push it back. Looking at that face, the induced current flows anticlockwise (to make a North pole facing you). When the magnet leaves, everything reverses: the near face becomes South and current flows clockwise as seen from that side.
Lenz's law decides which pole the coil must show (North or South) to oppose the change. The right-hand grip rule then converts that pole into a current direction: point your right thumb toward the required North face and your curled fingers show the current direction around the coil. Lenz picks the 'what', the hand rule reads the 'wire direction'.
Because of conservation of energy. If the induced current helped the change (attracting the approaching magnet), the magnet would speed up on its own forever and give free energy — a perpetual motion machine. That is impossible. So nature makes the current oppose the motion; you must do work against this opposing force, and that work becomes the electrical energy. Opposition is just energy conservation in disguise.
A strong bar magnet with its North pole facing right moves towards solenoid-2, coming from the side of solenoid-1 (the magnet is between the two coaxial solenoids, moving away from solenoid-1 and towards solenoid-2). Using Lenz's law, the directions of induced current in solenoid-1 and solenoid-2 respectively are (terminals labelled A, B on solenoid-1 and C, D on solenoid-2):
Try the real previous-year questions from this chapter — each with the answer and a full solution.
No, they work together. Faraday's law gives the SIZE of the induced emf (emf = -N dPhi/dt). Lenz's law explains the MINUS SIGN — it gives the DIRECTION (polarity) so the current always opposes the change in flux.
It means: if flux through the coil is increasing, the induced current makes its own magnetic field pointing opposite to fight the increase. If flux is decreasing, the induced current makes a field in the same direction to support it. The current never opposes the flux itself — it opposes the CHANGE.
No — it is a direct result OF energy conservation. Opposing the change means you must do work to keep the magnet moving, and that work becomes electrical energy. If the current helped instead, you would get free energy, which is impossible.
Approaching magnet: near face shows the SAME pole as the incoming pole (repel). Leaving magnet: near face shows the OPPOSITE pole (attract). Then use the right-hand grip rule to convert that pole into the current direction in the wire.
Yes. NEET regularly asks direction-of-current questions (2024 two-solenoid problem, loop moving out of a field). These are quick marks if you master the 'increasing or decreasing flux, then oppose' method — no long calculation needed.
