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← IIT-JEE 2007 · Paper 2
PhysicsAssertion and reason+3 / -1Question 12 of 66

IIT-JEE 2007 · Paper 2, Physics question 12

STATEMENT-1: A vertical iron rod has a coil of wire wound over it at the bottom end. An alternating current flows in the coil. The rod goes through a conducting ring as shown in the figure. The ring can float at a certain height above the coil.

because

STATEMENT-2: In the above situation, a current is induced in the ring which interacts with the horizontal component of the magnetic field to produce an average force in the upward direction.

A vertical iron rod with a coil of wire wound round its bottom end (leads going off to the left) and a conducting ring around the rod some height above the coil.
Choose one option
Answer and worked solution

Official answer: A

Induced current. The alternating flux through the ring induces a current that, by Lenz's law, opposes the change, so the ring and the coil repel on average.

Direction of the force. The force on the ring's current comes from the radial (horizontal) component of the coil's field: I dl⃗×B⃗radialI\,d\vec l\times\vec B_\text{radial} is vertical. Averaged over a cycle it points upward and can balance the weight. Statement 2 is true and explains Statement 1.

(A)

Topics:Faraday's and Lenz's lawsForce on a current-carrying conductor
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