Physics · Electromagnetic Induction · NEET
Treat each solenoid one at a time. First ask: is the magnet moving toward this coil or away from it? Moving toward = flux through the coil is increasing; moving away = flux is decreasing. Then apply Lenz's law: the coil makes a magnetic pole on its near face that opposes the change. Approaching magnet = the coil's near face becomes the SAME pole as the magnet's near face (to push it back). Leaving magnet = the coil's near face becomes the OPPOSITE pole (to pull it back). Finally use the right-hand rule to convert that pole into a current direction through the given terminals.
As the magnet moves away, the flux linked with that coil is decreasing. Lenz's law says the induced current opposes this decrease, so the coil tries to keep the flux up. To do that, its near face becomes the OPPOSITE pole to the magnet's near face (unlike poles attract), pulling the magnet back to hold on to its flux. This opposition is exactly why you must push the magnet — that mechanical work becomes the electrical energy (conservation of energy).
No — and this is the whole trap. One solenoid is losing flux and the other is gaining flux, so they oppose OPPOSITE changes and end up with opposite pole faces. That is why the answer is a pair like 'AB and DC', not 'AB and CD'. Never assume both coils behave the same just because it is one magnet.
Use the right-hand thumb rule for a solenoid: curl your right-hand fingers along the current in the windings, and your thumb points to the North face. So decide the pole Lenz's law requires, then choose the current direction (and hence which labelled terminal is entry vs exit) that produces that North face. The exam figure fixes the winding sense, so only one of AB or BA gives the needed pole.
A strong bar magnet (N-pole facing right) is moving towards solenoid-2, away from solenoid-1. The directions of the induced current in solenoid-1 and solenoid-2 respectively are:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Both. Faraday's law tells you an emf and current are induced because the flux is changing. Lenz's law tells you the DIRECTION of that current — it opposes the change. For 'which way does the current flow' questions like this two-solenoid PYQ, Lenz's law is the tool you actually use.
The logic is identical; only the poles flip. The leaving coil still attracts (opposite pole on its near face) and the approaching coil still repels (same pole on its near face). Just re-run the right-hand rule with the reversed pole, and both current directions reverse.
Students see one magnet and assume both solenoids react the same way, choosing 'AB and CD'. But the two coils sit on opposite sides of the moving magnet, so one is losing flux and one is gaining flux. Opposite changes give opposite current directions — the correct pair is 'AB and DC'.
No. Speed and magnet strength change only the SIZE of the induced emf and current (bigger dΦ/dt means bigger current). The direction is set purely by whether flux is increasing or decreasing, so it stays the same for a fast or slow magnet.
