College Physics (7th Edition)

Published by Pearson
ISBN 10: 0-32160-183-1
ISBN 13: 978-0-32160-183-4

Chapter 18 - Basic Electric Circuits - Learning Path Questions and Exercises - Conceptual Questions - Page 651: 6

Answer

The 40-W bulb will glow brighter. The brightness will be independent of the order since they are connected in series. None of the bulbs are at full power.

Work Step by Step

R of 60-W bulb $=R_{60}=\frac{120^{2}}{60}=240ohm$ R of 40-W bulb $=R_{40}=\frac{120^{2}}{40}=360ohm$ So, total resistance when they are in series = $240+360=600ohm$ Thus, $I=\frac{120}{600}=0.2A$ Power consumed by 60-W bulb = $P_{60}=I^{2}R=0.2^{2}\times 240=9.6W$ Power consumed by 40-W bulb = $P_{40}=I^{2}R=0.2^{2}\times 360=14.4W$ Therefore the 40-W bulb will glow brighter. The brightness will be independent of the order since they are connected in series. None of the bulbs are at full power.
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