Question

A bar magnet M is dropped so that it falls vertically through the coil C. The graph obtained for voltage produced across the coil V/S time is shown:-
Explain the shape of the graph.
Why is negative peak longer than positive peak ?

Answer 1

(i) As the bar magnet falls through the coil, magnetic flux linked with the coil increases, so the induced emf also increases across the coil.

Intially, rate of increase in flux increases, then it becomes maximum later on it decreases and becomes zero.

When the magnet exits the coil the emf decreses as well as induced emf polarity reverses. The rate of decrease of emf increases initially, becomes maximum an when the magnet is sufficiently far from the coil, the flux becomes zero and induced emf also becomes zero.

(ii) The negative peak is longer than positive peak as the magent moves out of the coil faster than it moves into the coil. As it enters the coil the back emf of the coil resists the fall of magnet. However, when it exits there is no back emf to resist the fall, hence gravity pulls the magnet faster.

Answer 2

Answer:

As the bar magnet falls via the coil, the magnetic flux connected with the coil increases, so the induced emf also rises across the coil.

Explanation:

(i) As the bar magnet falls via the coil, magnetic flux connected with the coil increases, so the induced emf also rises across the coil.

Initially, the rate of increase in flux increases, then it becomes utmost later on it declines and becomes zero.

When the magnet leaves the coil the emf falls as well as induced emf polarity reverses. The rate of decrease of emf increases originally becomes highest and when the magnet is adequately far from the coil, the flux becomes zero, and induced emf again becomes zero.

(ii) The negative peak is longer than the positive peak as the magnet proceeds out of the coil faster than it moves into the coil. as it enters the coil back emf of the coil opposes the fall of the magnet. However when it exists there is no back emf to resist the decline, hence gravity draws the magnet faster.

The graph is shown below,

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