Physics: Principles with Applications (7th Edition)

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

Chapter 19 - DC Circuits - Questions - Page 550: 23

Answer

The voltmeter has a very high resistance compared to the flashlight bulb. Also, over time, the battery’s internal resistance increases.

Work Step by Step

The terminal voltage of the battery is given by $\epsilon - Ir$, where r is the battery’s internal resistance. When a voltmeter is connected to the battery, very little current flows because of the meter’s high resistance, and the terminal voltage, as measured by the voltmeter, is very close to 1.5 volts. However, when the low resistance bulb is connected, a larger current I flows, and the voltage drop across the battery’s internal resistance can be quite large, leaving very little voltage drop across the bulb. The end result is a terminal voltage that is significantly lower than 1.5V, and a barely glowing bulb.
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