Heat Engines
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Q.
A Carnot engine operates between two reservoirs of temperature and . The engine performs of work per cycle. The heat energy in delivered by the engine to the low-temperature reservoir, in a cycle, is
Q. A steam engine delivers 5.4×108J of work per minute and services 3.6 × 109J of heat per minute from its boiler. What is the efficiency of the engine? How much heat is wasted per minute?
Q. 41. In a Camot engine, when heat is absorbed fromthe source, temperature of source(1) Increases(2) Decreases(3) Remains constant (4) Cannot say
Q. A fixed mass of gas undergoes a change represented by ABCDA as shown in figure. In some of the changes, work is done on the gas and in others, work is done by the gas. In which pair of the changes, work is done on the gas?
- AB and CD
- AB and BC
- BC and CD
- CD and DA
Q. A Carnot engine operates at an efficiency of 40% with the sink at 27∘C. Find the amount by which the temperature of the source must be increased in order to increase the efficiency by 10%.
- 600 K
- 100 K
- 500 K
- 300 K
Q. The area enclosed by a PV graph for one thermodynamic cycle of a heat engine is 610 J. The total thermal energy absorbed by the gas in one cycle is 1300 J. Determine the efficiency of the cycle.
- 47%
- 23%
- 9.4%
- 36.8%
Q. Two Carnot engines A and B are operated in series. The first one A receives heat from a source at temperature 800 K and rejects heat to a reservoir at temperature T K. The second engine B receives the heat rejected by the first engine and in turn rejects to a heat reservoir at temperature 300 K Find the value of temperature T if the efficiencies of two engines are equal.
(Take √6=2.45 for calculation)
(Take √6=2.45 for calculation)
- 550 K
- 300 K
- 25×104 K
- 490 K
Q. The maximum efficiency of a heat engine operating between 1000C and 250C is:
- None
- 20.11
- 22.2
- 25.17
Q. Two Carnot engines A and B are operated in series. The first engine, A, receives heat at 800 Kand rejects to a reservoir at temperature T. The second engine B receives the heat rejected by the first engine and in turn rejects to a heat reservoir at 300 K. Find the value of T, when the work outputs of the engines are equal.
- 0 K
- 1100 K
- 550 K
- 300 K
Q. The efficiency of a Carnot engine having source temperature 127∘C and sink temperature 27∘C is:
- 10%
- 25%
- 50%
- 60%
Q. An ideal gas is taken through a cyclic thermodynamic process through four steps. The amounts of heat involved in these steps are Q1=5960 J, Q2=−5585 J, Q3=−2980 J and Q4=3645 J respectively. The corresponding quantities of work involved are W1=2200 J, W2=−825 J, W3=−1100 J and W4 respectively . Find the efficiency of the cycle.
- 10.82 %
- 17.44 %
- 28.53 %
- 30.86 %
Q. A real heat engine has an efficiency of 40%. The work output of the engine is 100 kJ per cycle. How much energy is extracted from the high temperature reservoir per cycle ?
- 40 kJ
- 250 kJ
- 400 kJ
- Can be calculated only if the engine is a Carnot engine.
Q. An ideal gas is taken through a cycle 1231 (see figure) and the efficiency of the cycle was found to be 25%. When the same gas goes through the cycle 1341, the efficiency is 10%. Find the efficiency of the cycle 12341.
- 18.6 %
- 23.2 %
- 32.5 %
- 44 %
Q. If the sink temperature is decreased and the source temperature is held constant, then the efficiency of a Carnot engine can be:
- increased
- decreased
- remain constant
- None of these
Q. For which combination of temperatures the efficiency of Carnot's engine is highest?
- 80 K, 60 K
- 100 K, 80 K
- 60 K, 40 K
- 40 K, 20 K
Q. A carnot engine, whose efficiency is 40% takes in heat from a source maintained at a temperature of 500 K. It is desired to have an engine of efficiency 60%. Then, the intake temperature for the same exhaust (sink) must be
- efficiency of carnot engine cannot be made larger than 50%
- 1200 K
- 750 K
- 600 K
Q. In a Carnot heat engine, the temperature of source and sink are 500 K and 375 K respectively. The efficiency of engine is
- 75%
- 25%
- 33%
- −33%
Q. In which process in a Carnot's heat engine, heat (Q1) is absorbed from a heat source?
- Reversible isothermal expansion
- Reversible isothermal compression
- Reversible adiabatic expansion
- Reversible adiabatic compression
Q. A gas undergoes a cyclic process a→b→c→a which is as shown in the PV diagram. The process a→b is isothermal , b→c is adiabatic and c→a is a straight line on the P−V diagram. Work done in process ab and bc is 5 J and 4 J respectively. Calculate the efficiency of the cycle, if the area enclosed by the diagram abca in the figure is 3 J.
- 0.4
- 0.6
- 0.75
- 0.8
Q. A Carnot engine working between two temperatures has efficiency of 40%. Whan the temperature of the sink is reduced by 60oC, the efficiency increases to 55%. Calculate the two temperature in the first case.
Q. Calculate the theoretical maximum efficiency of a heat engine operating between 373K and 173K.
- 43.6%
- 33.6%
- 63.6%
- 53.6%
Q. An ideal reversible heat engine converts one sixth of the heat input into work. If the temperature of the sink is reduced by 62∘C, its efficiency is doubled. Find the temperature of the source and sink respectively (In Kelvin).
- 325, 375
- 372, 310
- 372, 248
- 472, 310
Q. Two engines are working in such a way that sink of one is source of the other. Their efficiencies are equal. Find the temperature of the sink of first if its source temperature is 927∘C and temperature of sink of the second is 27∘C
- 327 K
- 327∘C
- 600∘C
- none of these
Q. A fixed mass of gas undergoes a change represented by ABCDA as shown in figure. In some of the changes, work is done on the gas and in others, work is done by the gas. In which pair of the changes, work is done on the gas?
- AB and CD
- AB and BC
- BC and CD
- CD and DA
Q. An ideal reversible heat engine converts one sixth of the heat input into work. If the temperature of the sink is reduced by 62∘C, its efficiency is doubled. Find the temperature of the source and sink respectively (In Kelvin).
- 325, 375
- 372, 310
- 372, 248
- 472, 310