College Physics
1st Edition
ISBN: 9781938168000
Author: Paul Peter Urone, Roger Hinrichs
Publisher: OpenStax College
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Textbook Question
Chapter 21, Problem 11CQ
Before World War II, some radios got power through a “resistance cord" that had a significant resistance. Such a resistance cord reduces the voltage to a desired level for the radio’s tubes and the like, and it saves the expense of a transformer. Explain why resistance cords become warm and waste energy when the radio is on.
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Chapter 21 Solutions
College Physics
Ch. 21 - A switch has a variable resistance that is nearly...Ch. 21 - What is the voltage across the open switch in...Ch. 21 - There is a voltage across an open switch, such as...Ch. 21 - Why is the power dissipated by a closed switch,...Ch. 21 - A student in a physics lab mistakenly wired a...Ch. 21 - Knowing that the severity of a shock depends on...Ch. 21 - Would your headlights dim when you start your...Ch. 21 - Some strings of holiday lights are wired in series...Ch. 21 - If two household lightbulbs rated 60 W and 100 W...Ch. 21 - Suppose you are doing a physics lab that asks you...
Ch. 21 - Before World War II, some radios got power through...Ch. 21 - Some light bulbs have three power settings (not...Ch. 21 - Is every emf a potential difference? Is every...Ch. 21 - Explain which battery is doing the charging and...Ch. 21 - Given a battery, an assortment of resistors, and a...Ch. 21 - Two different 12-V automobile batteries on a store...Ch. 21 - What are the advantages and disadvantages of...Ch. 21 - Semitractor trucks use four large 12-V batteries....Ch. 21 - Call all of the currents going into the junction...Ch. 21 - Apply the junction rule to junction b in Figure...Ch. 21 - (a) What is the potential difference going from...Ch. 21 - Apply the loop rule to loop afedcba in Figure...Ch. 21 - Apply the loop rule to loops abgefa and cbgedc in...Ch. 21 - Why should you not connect an ammeter directly...Ch. 21 - Suppose you are using a multimeter (one designed...Ch. 21 - Specify the points to which you could connect a...Ch. 21 - To measure currents in Figure 21.49, you would...Ch. 21 - Why can a null measurement be more accurate than...Ch. 21 - If a potentiometer is used to measure cell emfs on...Ch. 21 - Regarding the units involved in the relationship t...Ch. 21 - The RC time constant in heart defibrillation is...Ch. 21 - When making an ECG measurement, it is important to...Ch. 21 - Draw two graphs of charge versus time on a...Ch. 21 - When charging a capacitor, as discussed in...Ch. 21 - When discharging a capacitor, as discussed in...Ch. 21 - Referring to Figure 21.38, draw a graph of...Ch. 21 - A long, inexpensive extension cord is connected...Ch. 21 - In Figure 21.41. does the graph indicate the time...Ch. 21 - An electronic apparatus may have large capacitors...Ch. 21 - (a) What is the resistance often 275-O resistors...Ch. 21 - (a) What is the resistance of a 1.00 102-O, a...Ch. 21 - What are the largest and smallest resistances you...Ch. 21 - An 1800-W toaster, a 1400-W electric frying pan,...Ch. 21 - Your car’s 30.0-W headlight and 2.40-kW starter...Ch. 21 - (a) Given a48.0-V battery and 24.0-O and 96.0-O...Ch. 21 - Referring to the example combining series and...Ch. 21 - Referring to Figure 21.6: (a) Calculate P3 and...Ch. 21 - Refer to Figure 21.7 and the discussion of lights...Ch. 21 - A 240-kV power transmission line carrying...Ch. 21 - Show that if two resistors R1and R2are combined...Ch. 21 - Unreasonable Results Two resistors, one having a...Ch. 21 - Unreasonable Results Two resistors, one having a...Ch. 21 - Standard automobile batteries have six lead-acid...Ch. 21 - Car bon-zinc dry cells (sometimes referred to as...Ch. 21 - What is the output voltage of a 3.0000-V lithium...Ch. 21 - (a) What is the terminal voltage of a large 1.54-V...Ch. 21 - What is the internal resistance of an automobile...Ch. 21 - (a) Find the terminal voltage of a 12.0-V...Ch. 21 - A car battery with a 12-V emf and an internal...Ch. 21 - The hot resistance of a flashlight bulb is 2.30 ,...Ch. 21 - The label or a portable radio recommends the use...Ch. 21 - An automobile starter motor has an equivalent...Ch. 21 - A child’s electronic toy is supplied by three...Ch. 21 - (a) What is the internal resistance of a voltage...Ch. 21 - A person with body resistance between his hands of...Ch. 21 - Electric fish generate current with biological...Ch. 21 - Integrated Concepts A 12.0-V emf automobile...Ch. 21 - Unreasonable Results A 1.58-V alkaline cell with a...Ch. 21 - Unreasonable Results (a) What is the internal...Ch. 21 - Apply the loop rule to loop abcdefgha in Figure...Ch. 21 - Apply the loop rule to loop aedcba in Figure...Ch. 21 - Verify the second equation in Example 21.5 by...Ch. 21 - Verify the third equation in Example 21.5 by...Ch. 21 - Apply the junction rule at point a in Figure...Ch. 21 - Apply the loop rule to loop abcdefghija in Figure...Ch. 21 - Apply the loop rule to loop akledcba in Figure...Ch. 21 - Find the currents flowing in the circuit in Figure...Ch. 21 - Solve Example 21.5, but use loop abcdefgha instead...Ch. 21 - Find the currents flowing in the circuit in Figure...Ch. 21 - Unreasonable Results Consider the circuit in...Ch. 21 - What is the sensitivity of the galvanometer (that...Ch. 21 - What is the sensitivity of the galvanometer (that...Ch. 21 - Find the resistance that must be placed in series...Ch. 21 - Find the resistance that must be placed in series...Ch. 21 - Find the resistance that must be placed in series...Ch. 21 - Find the resistance that must be placed in...Ch. 21 - Find the resistance that must be placed in series...Ch. 21 - Find the resistance that must be placed in...Ch. 21 - Suppose you measure the terminal voltage of a...Ch. 21 - Suppose you measure the terminal voltage of a...Ch. 21 - A certain ammeter has a resistance of 5.00X10-5 ...Ch. 21 - A 1,00-?O voltmeter is placed in parallel with a...Ch. 21 - A 0.0200- ammeter is placed in series with a...Ch. 21 - Unreasonable Results Suppose you have a 40.0-...Ch. 21 - Unreasonable Results (a) What resistance would you...Ch. 21 - What is the emf x of a cell being measured in a...Ch. 21 - Calculate the emfx of a dry cell for which a...Ch. 21 - When an unknown resistance Rxis placed in a...Ch. 21 - To what value must you adjust R3to balance a...Ch. 21 - (a) What is the unknown emfx in a potentiometer...Ch. 21 - Suppose you want to measure resistances in the...Ch. 21 - The timing device in an automobile’s intermittent...Ch. 21 - A heart pacemaker fires 72 times a minute, each...Ch. 21 - The duration of a photographic flash is related to...Ch. 21 - A 2.00- and a 7.50-F capacitor can be connected in...Ch. 21 - After two time constants, what percentage of the...Ch. 21 - A 500- resistor, an uncharged 1.50-F capacitor and...Ch. 21 - A heart defibrillator being used on a patient has...Ch. 21 - An ECG monitor must have an RC time constant less...Ch. 21 - Figure 21.55 shows how a bleeder resistor is used...Ch. 21 - Using the exact exponential treatment, find how...Ch. 21 - Using the exact exponential treatment, find how...Ch. 21 - Integrated Concepts If you wish to take a picture...Ch. 21 - Integrated Concepts A flashing lamp in a Christmas...Ch. 21 - Integrated Concepts A 160F capacitor charged to...Ch. 21 - Unreasonable Results (a) Calculate the capacitance...Ch. 21 - Construct Your Own Problem Consider a camera's...Ch. 21 - Construe! Your Own Problem Consider a rechargeable...
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