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A sample of an ideal gas with initial pressure p and volume V is taken through an isothermal expansion proceed during which the change in entropy is found to be ΔS. The universal gas constant is R. Then, the work done by the gas is given by :
By ideal gas equation,
pV = nRT ...(i)
and ...(ii)
Multiplying Equation (i) and (ii),
pVΔQ = nRΔS
⇒
∴ For isothermal expansion ΔV = 0
The correct answer is: (pVΔS)\(nR)
A Carnot engine operating between 27°C and 127°C has efficiency equal to
Select one:
T_{1} = (27 + 273)K = 300K
T_{2} = (127 + 273)K = 400K
Efficiency,
The correct answer is: 25%
TS diagram for a Carnot’s cycle is
Select one:
A Carnot cycle can be represented in a TS diagram, with T along the yaxis and S (entropy) along the xaxis. The isotherms are parallel horizontal lines at Tc and Th. The isentropes are parallel vertical lines (by definition they are of constant entropy). Thus, a Carnot cycle is represented by a rectangle.
The entropy of an isolated system
Select one:
The entropy of an isolated system increases in an irreversible process
The second law of thermodynamics states that the entropy of an isolated system never decreases because isolated systems always evolve toward thermodynamic equilibrium, a state with maximum entropy.
Hence the entropy of an isolated system increases in an irreversible process.
A Carnot cycle operates on a working substance between two reservoirs at temperatures T_{1} and T_{2} , where, T_{1} > T_{2} . Amount of heat Q_{1} is extracted from the reservoir at T_{1} and an amount Q_{2} is delivered to the reservoir at T_{2}. Which of the following statements is incorrect?
Carnot cycle is a reversible process ideally and in reversible processes the entropy of universe remains constant instead of increasing as in an irreversible process.
Two ends of a rod are kept at 127°C and 227°C. When 2000 cal of heat flows in this rod, then the change in entropy is
Select one:
Answer : d
Solution : T1 = 127 + 273 = 400K
T2 = 227 + 273 = 500K
dT = T2  T1
dT = 500  400 = 100
dS = dQ/dT
dS = 2000/100
dS = 20cal/K
At 0 K, fluids are assumed to have
Select one:
Entropy is the measurement of Randomness of a System. Increase in thermal energy increases the randomness and hence Entropy. Now decreasing the temperature of a fluid results in decrease in it's thermal energy which decreases the randomness of the system which in turn decreases the entropy of the fluid. Now there is a finite randomness at normal temperature in the fluid and as we proceed from a higher temperature to a lower temperature the randomness decreases so does the entropy. After continuing this process when we reach 0K further no thermal energy can be extracted from the fluid and hence the system can be said to be completely ordered and as the system is ordered (i.e zero randomness) the entropy is assumed to be zero.
The area of the Carnot cycle on a TS diagram represents
Select one:
A reversible heat engine can have 100% efficiency if the temperature of sink is
Select one:
Which of the following is a property of entropy?
Select one:
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