Fundamentholfundamenthol
JEE Main2026Jan 22, Shift 1Physics
Q.

Three identical coils , and are closely placed such that they share a common axis. is exactly midway. carries current in anti-clockwise direction while carries current in clockwise direction. An induced current flows through will be in clockwise direction when

  1. A

    and move with equal speeds away from

  2. B

    moves towards and moves away from

  3. C

    moves away from and moves towards

  4. D

    and move with equal speeds towards

Solution

Looking along the common axis from ’s side: is anti-clockwise, so its field through points away from (let’s call this ). is clockwise as viewed from its own side, so from ’s perspective ’s field also points in the direction through . So both coils contribute flux in the same direction through .

Net flux through : in .

For an induced current in to flow clockwise (as viewed from ’s side), the induced field inside must point in — meaning is opposing an increase in flux. So the net flux through must be increasing.

Bringing closer increases through ; moving away decreases through . For net flux to still increase, the gain from approaching must outweigh the loss from receding — this is what option (2) describes (and it matches the expected behaviour symmetric with the asymmetric current directions).

Among the four options, (2) is the correct case.

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