College Physics: A Strategic Approach (4th Edition)
4th Edition
ISBN: 9780134609034
Author: Randall D. Knight (Professor Emeritus), Brian Jones, Stuart Field
Publisher: PEARSON
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Textbook Question
Chapter 22, Problem 70MSPP
MCAT-Style Passage Problems
Lightbulb Failure
You’ve probably observed that the most common time for an incandescent lightbulb to fail is the moment when it is turned on. Let’s look at the properties of the bulb’s filament to see why this happens.
The current in the tungsten filament of a lightbulb heats the filament until it glows. The filament is so hot that some of the atoms on its surface fly off and end up sticking on a cooler part of the bulb. Thus the filament gets progressively thinner as the bulb ages. There will certainly be one spot on the filament that is a bit thinner than elsewhere. This thin segment will have a higher resistance than the surrounding filament. More power will be dissipated at this spot, so it won’t only be a thin spot, it also will be a hot spot.
Now, let’s look at the resistance of the filament. The graph in Figure P22.70 shows data for the current in a lightbulb as a function of the potential difference across it. The graph is not linear, so the filament is not an ohmic material with a constant resistance. However, we can define the resistance at any particular potential difference ∆V to be R = ∆V/I. This ratio, and hence the resistance, increases with ∆V and thus with temperature.
Figure P22. 70
When the bulb is turned on, the filament is cold and its resistance is much lower than during normal, high-temperature operation. The low resistance causes a surge of higher-than-normal current lasting a fraction of a second until the filament heats up. Because power dissipation is I2R, the power dissipated during this first fraction of a second is much larger than the bulb’s rated power. This current surge concentrates the power dissipation at the high-resistance thin spot, perhaps melting it and breaking the filament.
70. For the bulb in Figure P22.70, what is the approximate resistance of the bulb at a potential difference of 6.0 V?
A. 7.0 Ω
B. 17 Ω
C. 27 Ω
D. 37 Ω
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Chapter 22 Solutions
College Physics: A Strategic Approach (4th Edition)
Ch. 22 - Prob. 2CQCh. 22 - Prob. 3CQCh. 22 - Prob. 4CQCh. 22 - All wires in Figure Q22.519 are made of the same...Ch. 22 - A wire carries a 4 A current. What is the current...Ch. 22 - Prob. 7CQCh. 22 - Cells in the nervous system have a potential...Ch. 22 - a. Which directionclockwise or...Ch. 22 - Prob. 10CQCh. 22 - Prob. 11CQ
Ch. 22 - The two circuits in Figure Q22.12 use identical...Ch. 22 - The two circuits in Figure Q22.13 use identical...Ch. 22 - Prob. 14CQCh. 22 - Rank in order, from largest to smallest, the...Ch. 22 - The circuit in Figure Q22.16 has three batteries...Ch. 22 - Prob. 17CQCh. 22 - Prob. 18CQCh. 22 - Over time, atoms boil off the hot filament in an...Ch. 22 - Prob. 20CQCh. 22 - A 100 W lightbulb is brighter than a 60 W...Ch. 22 - Lightbulbs are typically rated by their power...Ch. 22 - Lightbulbs are typically rated by their power...Ch. 22 - A copper wire is stretched so that its length...Ch. 22 - The potential difference across a length of wire...Ch. 22 - Prob. 26MCQCh. 22 - A resistor connected to a 3.0 V battery dissipates...Ch. 22 - If a 1.5 V battery stores 5.0 kJ of energy (a...Ch. 22 - Figure Q22.29 shows a side view of a wire of...Ch. 22 - A person gains weight by adding fatand therefore...Ch. 22 - Prob. 31MCQCh. 22 - The current in an electric hair dryer is 10 A. How...Ch. 22 - Prob. 2PCh. 22 - Three wires meet at a junction. Wire 1 has a...Ch. 22 - When a nerve cell depolarizes, charge is...Ch. 22 - A wire carries a 15 A current. How many electrons...Ch. 22 - In a typical lightning strike, 2.5 C flows from...Ch. 22 - Prob. 7PCh. 22 - In an ionic solution, 5.0 1015 positive ions with...Ch. 22 - Prob. 9PCh. 22 - What are the values of currents IB and IC in...Ch. 22 - The currents through several segments of a wire...Ch. 22 - How much electric potential energy does 1.0 C of...Ch. 22 - What is the emf of a battery that increases the...Ch. 22 - A 9.0 V battery supplies a 2.5 mA current to a...Ch. 22 - Prob. 16PCh. 22 - An electric catfish can generate a significant...Ch. 22 - A Wire with resistance R is connected to the...Ch. 22 - Wires 1 and 2 are made of the same metal. Wire 2...Ch. 22 - Prob. 20PCh. 22 - Resistivity measurements on the leaves of corn...Ch. 22 - Prob. 22PCh. 22 - A motorcyclist is making an electric vest that,...Ch. 22 - Prob. 24PCh. 22 - A 3.0 V potential difference is applied between...Ch. 22 - Prob. 26PCh. 22 - Prob. 27PCh. 22 - Prob. 28PCh. 22 - Figure P22.29 shows the...Ch. 22 - Figure P22.30 is a...Ch. 22 - In Example 22.6 the length of a 60 W, 240 ...Ch. 22 - The electric field inside a 30-cm-long copper wire...Ch. 22 - A copper wire is 1.0 mm in diameter and carries a...Ch. 22 - Two identical lightbulbs are connected in series...Ch. 22 - Prob. 35PCh. 22 - a. What is the resistance of a 1500 W (120 V) hair...Ch. 22 - Prob. 37PCh. 22 - A 70 W electric blanket runs at 18 V. a. What is...Ch. 22 - A 60-cm-long heating wire is connected to a 120 V...Ch. 22 - An electric eel develops a potential difference of...Ch. 22 - Prob. 41PCh. 22 - A 3.0 V battery powers a flashlight bulb that has...Ch. 22 - A heating element in a toaster dissipates 900 W...Ch. 22 - Prob. 44GPCh. 22 - Prob. 45GPCh. 22 - The hot dog cooker described in the chapter heats...Ch. 22 - Air isnt a perfect electric insulator, but it has...Ch. 22 - The biochemistry that takes place inside cells...Ch. 22 - High-resolution measurements have shown that an...Ch. 22 - When an ion channel opens in a cell wall (see...Ch. 22 - The total charge a battery can supply is rated in...Ch. 22 - Prob. 52GPCh. 22 - The heating element of a simple heater consists of...Ch. 22 - Variations in the resistivity of blood can give...Ch. 22 - A 40 W (120 V) lightbulb has a tungsten filament...Ch. 22 - Prob. 56GPCh. 22 - When the starter motor on a car is engaged, there...Ch. 22 - Prob. 58GPCh. 22 - The two segments of the wire in Figure P22.59 have...Ch. 22 - Prob. 60GPCh. 22 - Prob. 61GPCh. 22 - Prob. 62GPCh. 22 - Prob. 63GPCh. 22 - Prob. 64GPCh. 22 - An immersion heater used to boil water for a...Ch. 22 - The graph in Figure P22.66 shows the current...Ch. 22 - Its possible to estimate the percentage of fat in...Ch. 22 - If you touch the two terminals of a power supply...Ch. 22 - The average resistivity of the human body (apart...Ch. 22 - MCAT-Style Passage Problems Lightbulb Failure...Ch. 22 - MCAT-Style Passage Problems Lightbulb Failure...Ch. 22 - MCAT-Style Passage Problems Lightbulb Failure...Ch. 22 - MCAT-Style Passage Problems Lightbulb Failure...
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