CBSE 2025, Set 3

Question

A soft iron rod X is allowed to fall on the two poles of a U shaped permanent magnet as shown in figure. A coil is wrapped over one arm of the U shaped magnet.
![U-shaped magnet with falling soft iron rod](https://media.edvaya.com/wp-content/uploads/cbse-class-12-physics-2025-set-3-od-q5.webp)
During fall of the rod, the current in the coil will be: A). clockwise current B). anti-clockwise current C). alternating current D). zero

Edvaya · Accepted Answer

The correct answer is anti-clockwise current. As the soft iron rod $X$ falls towards the poles of the U-shaped magnet, the air gap decreases. Soft iron has high permeability, which provides a path of low reluctance. This causes the downward magnetic flux ($\Phi$) passing through the right arm (South pole) of the magnet to **increase**. According to **Lenz's Law**, the induced current in the coil will flow in a direction that opposes this increase in downward magnetic flux. To oppose it, the induced current must create an *upward* magnetic field.

Using the Right-Hand Grip Rule on the coil (viewed from the top), the current must flow in an **anti-clockwise** direction to produce an upward magnetic field.

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Physics > Magnetism Induction And Alternating Current > Electromagnetic Induction

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