In answering all questions on this exam, use the convention that CircleDot indic

Question

In answering all questions on this exam, use the convention that CircleDot indicates a vector pointing out of the page and CircleTimes indicates a vector pointing into the page. A metal ring is moved away from a bar magnet as shown. Is there a current induced in the copper loop? If so, in which direction? If not, why not? Two identical metal rings each have currents in them as shown. The current in the loop on the Left is twice the magnitude of the current in the loop on the right. Is there a force on the left loop by the right loop? If so, in which direction? If not, why not? Explain your reasoning. Is the force on the left loop by the right loop greater than, less than, or equal to the magnitude of the force on the right loop by the left loop? Explain.

Explanation / Answer

1)

Considering the eye on the axis of the ring and to the left of the ring.

Flux through the ring is outward and is decreasing as the ring is moving away from magnet.

By Lenz's law , induced emf and induced current are in such a direction that the cause of change of flux is opposed.

That is more outward flux must be created ,hence the induced current is counterclockwise.

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2)

i)For an observer to the left of both rings, on the axis of rings the currentin the left ring is clockwise and current in the right ring is counter clockwise. Hence the magnetic dipole moment of left ring points to the right and magnetic dipole moment of right ring points to the left. That is their north poles face each other. They repel each other. Hence force on the left ring by the right ring is to the left.

ii)The forces that rings exert on each other are equal in magnitude and opposite in direction.

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