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 - General Problems - Page 524: 82

Answer

$2000^{\circ}C$.

Work Step by Step

We can calculate the resistance of the filament when the flashlight is on and the filament is hot. $$R=\frac{V}{I}=\frac{3.0V}{0.20A}=15\Omega$$ Relate this resistance to the room temperature resistance to find the operating temperature. $$R=R_0(1+\alpha(T-T_0))$$ $$T=T_0+\frac{1}{\alpha}(\frac{R}{R_0}-1)= 20^{\circ}C+\frac{1}{0.0045C^{-1}}(\frac{15\Omega}{1.5\Omega}-1)\approx 2000^{\circ}C $$
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