Physics: Principles with Applications (7th Edition)

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

Chapter 18 - Electric Currents - Questions: 10

Answer

The cool filament in a bulb that has been off has lower resistance than the heated filament of a bulb that has been on for some time.

Work Step by Step

Before an “old-fashioned” lightbulb is turned on, the filament is cool and has a relatively low resistance compared to when it is hot (the resistivity rises with temperature). So, when electricity is first applied, the low R means a spike in current, and in power. This can heat up and vaporize the filament, ending the bulb’s life. When the bulb has been on for a few seconds, the filament has reached its final high temperature, with a high resistance and a steady low current. There is little thermal stress on the filament and the bulb is less likely to die under these conditions.
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