Physics: Principles with Applications (7th Edition)

Published by Pearson
ISBN 10: 0-32162-592-7
ISBN 13: 978-0-32162-592-2

Chapter 21 - Electromagnetic Induction and Faraday's Law - Questions - Page 618: 18

Answer

The speed of the magnet in case A will be slower than that in case B, when they strike the floor.

Work Step by Step

Magnetic field lines point away from the north pole of the magnet. In case A, as the bar magnet falls toward the loop, the magnetic flux in the ring is increasing. The number of magnetic field lines passing downward through the loop increases with time. By Faraday’s Law, the changing flux induces a current to flow around the ring, which in turn creates an opposing magnetic field (Lenz’s law) that will slow the motion of the falling magnet. This braking effect, similar to eddy current braking, acts like a drag force upon the magnet. Later, after the middle of the magnet passes through the loop, the induced current reverses direction and attracts the falling magnet upward, again slowing it down. If there is no loop, then we are in case B, none of the above applies, and the falling motion of the magnet is unhindered. The speed of the magnet in case A will be slower than that in case B, when they strike the floor.
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