   Chapter 18, Problem 53AP

Chapter
Section
Textbook Problem

A circuit consists of three identical lamps, each of resistance R, connected to a battery as in Figure P18.53. (a) Calculate an expression for the equivalent resistance of the circuit when the switch is open. Repeat the calculation when the switch is closed. (b) Write an expression for the power supplied by the battery when the switch is open. Repeat the calculation when the switch is closed. (c) Using the results already obtained, explain what happens to the brightness of the lamps when the switch is closed. Figure P18.53

To determine
The value of R.

Explanation

When the switch is closed, the circuit can be reduced as,

When the circuit is open, the circuit can be reduced as,

The resistance between the points a and b drops to one-half of its original value when the switch is closed. Therefore,

R+18Ω=12(R+</

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