Physics Technology Update (4th Edition)

Published by Pearson
ISBN 10: 0-32190-308-0
ISBN 13: 978-0-32190-308-2

Chapter 21 - Electric Current and Direct-Current Circuits - Problems and Conceptual Exercises - Page 757: 50

Answer

Two bulbs can be connected.

Work Step by Step

We know that the equivalent resistance of the entire circuit is given as $ R_{eq}=\frac{V}{I_{max}}$ The resistance of one light bulb is $ R=\frac{V^2}{P}$ Let $ n $ be the number of light bulbs required for the circuit $\implies \frac{1}{R_{eq}}=\frac{n}{R}$ This can be rearranged as: $ n=\frac{R}{R_{eq}}$ $\implies n=(\frac{V^2}{P})(\frac{I_{max}}{V})$ $\implies n=\frac{VI_{max}}{P}$ We plug in the known values to obtain: $ n=\frac{(85V)(2.1A)}{65W}$ $ n=2.7$ Thus, only two bulbs can be connected in parallel before the total current exceeds $2.1A $.
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