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 - Search and Learn - Page 624: 1

Answer

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Work Step by Step

a. Areas with water where the skin may get wet (kitchens, bathrooms, garages and outdoor areas) are required to have ground fault circuit interrupters. Wet skin has a much smaller resistance than dry skin, so if one accidentally makes contact with a live wire while grounded, it is more dangerous to do so when your skin is wet because the current that flows can be considerably larger. b. GFCIs work using Ampere’s law and Kirchhoff’s current law. Two wires from the power source pass through an iron ring. Under normal conditions, the current going out should exactly equal the current going in, so the net current through the ring is zero. No magnetic field is induced in the ring, by Ampere’s Law. If an unfortunate human makes contact with the live wire and grounds some of the current, then the current going out from the outlet is greater than the return current, by Kirchhoff’s current law. The enclosed current is nonzero, and by Ampere’s Law, an alternating magnetic field is created in the ring. The changing flux induces an emf and a current in a small sensing wire, which “immediately” cuts off the power. Fuses and circuit breakers are designed to shut off the power if too much current is flowing through the wires, preventing overheating in the wires and electrical fires, but even a current much smaller than their threshold can injure a human. GFCIs are more sensitive and they act more quickly than fuses and circuit breakers. Together, circuit breakers and GFCIs protect property and life.
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