University Physics with Modern Physics (14th Edition)
14th Edition
ISBN: 9780321973610
Author: Hugh D. Young, Roger A. Freedman
Publisher: PEARSON
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Textbook Question
Chapter 25, Problem 25.24DQ
The text states that good thermal conductors are also good electrical conductors. If so, why don’t the cords used to connect toasters, irons, and similar heat-producing appliances get hot by
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A close analogy exists between the flow of energy by heat
because of a temperature difference (see Section 19.6) and
the flow of electric charge because of a potential difference.
In a metal, energy dQ and electrical charge dq are both
transported by free electrons. Consequently, a good electri-
cal conductor is usually a good thermal conductor as well.
Consider a thin conducting slab of thickness dx, area A,
and electrical conductivity ơ, with a potential difference dV
between opposite faces. (a) Show that the current I = dq/dt
is given by the equation on the left:
Charge conduction
Thermal conduction
dq
= oA
dt
dT
kA
dt
dQ
AP
dx
dx
In the analogous thermal conduction equation on the right
(Eq. 19.17), the rate dQ/dt of energy flow by heat (in SI units
of joules per second) is due to a temperature gradient
dT/dx in a material of thermal conductivity k. (b) State anal-
ogous rules relating the direction of the electric current to
the change in potential and relating the direction of…
A close analogy exists between the flow of energy by heat because of a temperature difference (see Section 20.7) and the
flow of electric charge because of a potential difference. In a metal, energy dQ and electrical charge dq are both
transported by free electrons. Consequently, a good electrical conductor is usually a good thermal conductor as well.
Consider a thin conducting slab of thickness dx, area A, and electrical conductivity o, with a potential difference dv
between opposite faces. (a) Show that the current I = dq/dt is given by the equation on the left:
Charge conduction Thermal conduction
dq
TA
dt
JdT|
kA
dt
dQ
| dx
|AP|
|dx
In the analogous thermal conduction equation on the right (Eq. 20.15), the rate dQ/dt of energy flow by heat (in Sl units of
joules per second) is due to a temperature gradient dT/dx in a material of thermal conductivity k. (b) State analogous rules
relating the direction of the electric current to the change in potential and relating the direction of…
An incandescent lightbulb is an inexpensive but highly inefficient device that converts electrical energy into light. It converts about 10 percent of the electrical energy it consumes into light while converting the remaining 90 percent into heat. The glass bulb of the lamp heats up very quickly as a result of absorbing all that heat and dissipating it to the surroundings by convection and radiation. Consider an 8-cm-diameter 60-W lightbulb in a room at 25°C. The emissivity of the glass is 0.9. Assuming that 10 percent of the energy passes through the glass bulb as light with negligible absorption and the rest of the energy is absorbed and dissipated by the bulb itself by natural convection and radiation, determine the equilibrium temperature of the glass bulb. Assume the interior surfaces of the room to be at room temperature.
Chapter 25 Solutions
University Physics with Modern Physics (14th Edition)
Ch. 25.1 - Suppose we replaced the wire in Example 25.1 with...Ch. 25.2 - Prob. 25.2TYUCh. 25.3 - Suppose you increase the voltage across the copper...Ch. 25.4 - Rank the following circuits in order from highest...Ch. 25.5 - Rank the following circuits in order from highest...Ch. 25.6 - Which of the following factors will, if increased,...Ch. 25 - The definition of resistivity ( = E/J) implies...Ch. 25 - A cylindrical rod has resistance R. If we triple...Ch. 25 - A cylindrical rod has resistivity . If we triple...Ch. 25 - Two copper wires with different diameters are...
Ch. 25 - When is a 1.5-V AAA battery not actually a 1.5-V...Ch. 25 - Can the potential difference between the terminals...Ch. 25 - A rule of thumb used to determine the internal...Ch. 25 - Batteries are always labeled with their emf; for...Ch. 25 - We have seen that a coulomb is an enormous amount...Ch. 25 - Electrons in an electric circuit pass through a...Ch. 25 - Temperature coefficients of resistivity are given...Ch. 25 - Which of the graphs in Fig. Q25.12 best...Ch. 25 - Why does an electric light bulb nearly always burn...Ch. 25 - A light bulb glows because it has resistance. The...Ch. 25 - (See Discussion Question Q25.14.) An ideal ammeter...Ch. 25 - (See Discussion Question Q25.14.) Will a light...Ch. 25 - The energy that can be extracted from a storage...Ch. 25 - Eight flashlight batteries in series have an cmf...Ch. 25 - Small aircraft often have 24-V electrical systems...Ch. 25 - Long-distance, electric-power, transmission lines...Ch. 25 - Ordinary household electric lines in North America...Ch. 25 - A fuse is a device designed to break a circuit,...Ch. 25 - High-voltage power supplies are sometimes designed...Ch. 25 - The text states that good thermal conductors are...Ch. 25 - Lightning Strikes. During lightning strikes from a...Ch. 25 - A silver wire 2.6 mm in diameter transfers a...Ch. 25 - A 5.00-A current runs through a 12-gauge copper...Ch. 25 - An 18-gauge copper wire (diameter 1.02 mm) carries...Ch. 25 - Copper has 8.5 1028 free electrons per cubic...Ch. 25 - Prob. 25.6ECh. 25 - CALC The current in a wire varies with time...Ch. 25 - Current passes through a solution of sodium...Ch. 25 - BIO Transmission of Nerve Impulses. Nerve cells...Ch. 25 - (a) At room temperature, what is the strength of...Ch. 25 - A 1.50-m cylindrical rod of diameter 0.500 cm is...Ch. 25 - A copper wire has a square cross section 2.3 mm on...Ch. 25 - Prob. 25.13ECh. 25 - Prob. 25.14ECh. 25 - A cylindrical tungsten filament 15.0 cm long with...Ch. 25 - A ductile metal wire has resistance R. What will...Ch. 25 - Prob. 25.17ECh. 25 - Prob. 25.18ECh. 25 - Prob. 25.19ECh. 25 - Prob. 25.20ECh. 25 - A current-carrying gold wire has diameter 0.84 mm....Ch. 25 - A hollow aluminum cylinder is 2.50 m long and has...Ch. 25 - Prob. 25.23ECh. 25 - A carbon resistor is to be used as a thermometer....Ch. 25 - A copper transmission cable 100 km long and 10.0...Ch. 25 - Consider the circuit shown in Fig. E25.26. The...Ch. 25 - An ideal voltmeter V is connected to a 2.0-11...Ch. 25 - An idealized ammeter is connected to a battery as...Ch. 25 - When switch S in Fig. E25.29 is open, the...Ch. 25 - The circuit shown in Fig. E25.30 contains two...Ch. 25 - In the circuit shown in Fig. E25.30, the 16.0-V...Ch. 25 - In the circuit of Fig. E25.30, the 5.0- resistor...Ch. 25 - The circuit shown in Fig. E25.33 contains two...Ch. 25 - When a resistor with resistance R is connected to...Ch. 25 - Light Bulbs. The power rating of a light bulb...Ch. 25 - If a 75-W" bulb (see Problem 25.35) is connected...Ch. 25 - European Light Bulb. In Europe the standard...Ch. 25 - A battery-powered global positioning system (GPS)...Ch. 25 - Consider the circuit of Fig. E25.30. (a) What is...Ch. 25 - BIO Electric Eels. Electric eels generate electric...Ch. 25 - BIO Treatment of Heart Failure. A heart...Ch. 25 - The battery for a certain cell phone is rated at...Ch. 25 - Prob. 25.43ECh. 25 - An idealized voltmeter is connected across the...Ch. 25 - A 25.0- bulb is connected across the terminals of...Ch. 25 - A typical small flashlight contains two batteries,...Ch. 25 - In the circuit in Fig. E25.47, find (a) the rate...Ch. 25 - A 540-W electric heater is designed to operate...Ch. 25 - Prob. 25.49ECh. 25 - In an ionic solution, a current consists of Ca2+...Ch. 25 - An electrical conductor designed to carry large...Ch. 25 - An overhead transmission cable for electrical...Ch. 25 - On your first day at work as an electrical...Ch. 25 - A 2.0-m length of wire is made by welding the end...Ch. 25 - A 3.00-m length of copper wire at 20 C has a...Ch. 25 - A heating clement made of tungsten wire is...Ch. 25 - CP BIO Struck by Lightning. Lightning strikes can...Ch. 25 - A resistor with resistance R is connected to a...Ch. 25 - CALC A material of resistivity is formed into a...Ch. 25 - CALC The region between two concentric conducting...Ch. 25 - The potential difference across the terminals of a...Ch. 25 - (a) What is the potential difference Vad in the...Ch. 25 - BIO The average bulk resistivity of the human body...Ch. 25 - BIO A person with body resistance between his...Ch. 25 - A typical cost for electrical power is 0,120 per...Ch. 25 - In the circuit shown in Fig. P25.66, R is a...Ch. 25 - A Nonideal Ammeter. Unlike the idealized ammeter...Ch. 25 - A cylindrical copper cable 1.50 km long is...Ch. 25 - CALC A 1.50-m cylinder of radius 1.10 cm is made...Ch. 25 - Compact Fluorescent Bulbs. Compact fluorescent...Ch. 25 - Prob. 25.71PCh. 25 - CP Consider the circuit shown in Fig. P25.72. The...Ch. 25 - CP Consider the circuit shown in Fig. P25.73. The...Ch. 25 - DATA An external resistor R is connected between...Ch. 25 - DATA The voltage drop Vab across each of resistors...Ch. 25 - DATA According to the U.S. National Electrical...Ch. 25 - Prob. 25.77CPCh. 25 - An external resistor with resistance R is...Ch. 25 - BIO SPIDERWEB CONDUCTIVITY. Some types of spiders...Ch. 25 - BIO SPIDERWEB CONDUCTIVITY. Some types of spiders...Ch. 25 - BIO SPIDERWEB CONDUCTIVITY. Some types of spiders...Ch. 25 - BIO SPIDERWEB CONDUCTIVITY. Some types of spiders...
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