Which cycle is more efficient?O a → c → d → a, because the cycle takes only three stepsO a → b → c → d → a, because the cycle takes a greater number of stepsO a → c - d → a, because the cycle does more useful workO a → b → c → d → a, because the cycle does more useful worksame for both A heat engine can follow one of two cycles that expand and compress an ideal gas, as shown in the figure. Each cycle takes thesame amount of heat to do the work.3T.|2TToC.

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Which cycle is more efficient? a → c → d → a, because the cycle takes only three steps O a → b → c → d → a, because the cycle takes a greater number of steps a → c → d → a, because the cycle does more useful work a → b → c → d → a, because the cycle does more useful work same for both

Which cycle is more efficient? a → c → d → a, because the cycle takes only three steps O a → b → c → d → a, because the cycle takes a greater number of steps a → c → d → a, because the cycle does more useful work a → b → c → d → a, because the cycle does more useful work same for both

University Physics Volume 2

18th Edition

ISBN:9781938168161

Author:OpenStax

Publisher:OpenStax

Chapter4: The Second Law Of Thermodynamics

Section: Chapter Questions

Problem 81AP: A Carnot engine working between two heat baths of temperatures 600 K and 273 K completes each cycle...

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Steam locomotives have an efficiency of 17.0% and operate with a hot steam temperature of 425C. (a) What would the cold reservoir temperature be if this were a Carnot engine? (b) What would the maximum eficiency of this steam engine be if its cold reservoir temperature were 150C ?
A heat pump has a coefficient of performance of 3.80 and operates with a power consumption of 7.03 103 W. (a) How much energy does it deliver into a home during 8.00 h of continuous operation? (b) How much energy does it extract from the outside air?
An ideal gas expands isothermally along AB and does 700 J of work (see below). (a) How much heat does the gas exchange along AB? (b) The gas then expands adiabatically along BC and does 400 J of work. When the gas returns to A along CA, it exhausts 100 J of heat to its surroundings. How much work is done on the gas along this path?
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Check your Understanding Show that QhQh=QcQc for the hypothetical engine of Figure 4.10 The second property to be demonstrated is that all reversible engines operating between the same two reservoirs have the same efficiency. To this, stat with the two engines D and E of Figure 4.10 (a), which are operating between two common heat reservoirs at temperatures Th and Tc . First, assume that D is a reversible engine and that E is a hypothetical irreversible engine that has a higher efficiency than D. If both engines perform the same amount of work W per cycle, it follows from Equation 4.2 that QhQh . It then follows from the first law that QcQc . Figure 4.10 (a) Two uncoupled engines D and E working between the same reservoirs. (b) The engines, With D working reverse. Suppose the cycle of D is so that it operates as a refrigerator, and the two engines are coupled such that the work output of E is used to drive D, as shown in Figure 4.10(b). Since QhQh and QcQc , the net result of each cycle is equivalent to a spontaneous transfer of heat from the cold reservoir to the hot reservoir, a process second law does not allow. The original assumption must therefore be wrong, and it is impossible to construct an irreversible engine such that E is more efficient than the reversible engine D. Now it is quite easy to demonstrate that the efficiencies of all reversible engines operating between the same reservoirs are equal. Suppose that D and E are reversible engines. If they are as shown in Figure 4.10(b), the efficiency of E cannot be greater than the efficiency of D, or second law would violated. If both engines are then reversed, the same reasoning implies that the efficiency of D cannot be greater than the efficiency of E. Combining these results leads to the conclusion that all reversible engines working between same two reservoirs have the same efficiency.
When a gas expands along AB (see below), it does 500 J of work and absorbs 250 J of heat. When the gas expands along AC, it does 700 J of work and absorbs 300 J of heat. (a) How much heat does the gas exchange along BC? (b) When the gas makes the transmission from C to A along CDA, 800 J of work are done on it from C to D. How much heat does it exchange along CDA?
Check Your Understanding What is the efficiency of a perfect heat engine? What is the coefficient of performance of a perfect refrigerator?