2 2. Suppose that a bar magnet falls through a conducting hoop of wire with its

Question

2 2. Suppose that a bar magnet falls through a conducting hoop of wire with its north pole facing downward. Three consecutive snapshots of its descent are shown below. For each snapshot, state whether: a) the magnetic flux through the loop is upward, downward, or zero; b) the induced current is clockwise, counterclockwise, or zero, from the point of view of an observer looking down from above the loop. Make a qualitative sketch of the induced current versus time (taking counterclockwise as seen from above to be the positive direction), and label times 1, 2 and 3 on this plot. 35

Explanation / Answer

a) In snapshot 1, magnetic flux is downward. In 2, it is zero (as magnet is centered) and in 3, it is upward.

b) using Lenz's law, the face of the loop towards the magnet (if magnet is approaching), will develop the same pole (north or south) so as to oppose the change in magnetic flux.

So, in situation 1, north pole will be developed, hence the current would be anticlockwise.

in situation 2, no change in magnetic flux, current is zero.

in situation 3, south pole will be developed on upper side, thus, the current would be clockwise.

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