# Heat Engines

## Trending Questions

**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 %
- 30.86 %
- 17.44 %
- 28.53 %

**Q.**

What is the first three laws of thermodynamics?

**Q.**

What are the first and second laws of thermodynamics?

**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.**Helium gas goes through a cycle ABCDA (consisting of two isochoric and two isobaric lines) as shown in figure. Efficiency of this cycle is nearly:

[Assume the gas to be an ideal gas]

- 15.4%
- 10.5%
- 9.1%
- 12.5%

**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.**An ideal monoatomic gas undergoes the cyclic process ABCDA as shown in the figure. The efficiency of the cycle is

- 28.6%
- 19.04%
- 46.8%
- 62.3%

**Q.**A Carnot heat engine works between the temperatures 427∘C and 27∘C. What amount of heat should it consume per second to deliver mechanical work at the rate of 1.0 kW?

- 418 cal/s
- 41.8 cal/s
- 4.18 cal/s
- 0.418 cal/s

**Q.**In a Carnot heat engine, the temperature of source and sink are 500 K and 375 K. If the engine consumes 25×105 J per cycle, then work done by engine per cycle is

- 6.25×105 J
- 100×105 J
- 2.5×105 J
- 0.625×105 J

**Q.**The P−V diagram of a diatomic ideal gas system going under cyclic process as shown in figure. The work done during an adiabatic process CD is (use γ=1.4):

- –400 J
- –500 J
- 200 J
- 400 J

**Q.**

A pump motor is used to deliver water at a certain rate from a given pipe to a certain height. To obtain twice as much water from the same pipe in the same time, power of the motor has to be increased to

16 times

4 times

8 times

2 times

**Q.**The number of molecules in one litre of an ideal gas at 300 K and 2 atmospheric pressure with mean kinetic energy 2×10–9 J per molecule is :

- 3×1011
- 1.5×1011
- 0.75×1011
- 6×1011

**Q.**A cyclic process ABCA is shown in the V-T diagram. Process on the P-V diagram is

**Q.**In a Carnot heat engine, the temperature of source and sink are 827∘C and 27∘C. If the engine consumes 33 kJ per cycle, then the heat rejected to the sink per cycle is

- 9 kJ
- 24 kJ
- 11 kJ
- 10 kJ

**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).

- 372, 310
- 372, 248
- 472, 310
- 325, 375

**Q.**

What is the full form of ITUS?

**Q.**An engine operates by taking a monoatomic ideal gas through the cycle shown in the figure. The percentage efficiency of the engine is close to ______.

**Q.**Number of molecules in a volume of 4 cm3 of a perfect monoatomic gas at some temperature T and at a pressure of 2 cm of mercury is close to ?

(Given, mean kinetic energy of a molecule (at T) is 4×10−14 erg, g=980 cm/s2, density of mercury =13.6 g/cm3)

- 4.0×1018
- 4.0×1016
- 5.8×1016
- 5.8×1018

**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%
- 36.8%
- 9.4%

**Q.**One mole of a monoatomic gas of molar mass M undergoes a cyclic process as shown in the figure. Here, ρ is the density and P is the pressure of the gas. Find the efficiency of the cycle.

- 35(1−ln2)
- 35ln2
- 2 ln25
- 25(1−ln2)

**Q.**One mole of a diatomic ideal gas (γ=1.4) is taken through a cyclic process starting from point A. The process A→B is an adiabatic compression, B→C is an isobaric expansion, C→D is an adibatic expansion and D→A is an isochoric process. The volume ratios are VAVB=16, VCVB=2 and temperature TA=27∘C. Find the efficiency of the cycle.

- 32.84 %
- 61.40 %
- 28.56 %
- 35.61 %

**Q.**An ideal gas is taken through the cycle ABCA a shown in the P-V diagram. The total work done by the gas during the cycle is

- pV
- 3pV
- 6pV
- 2pV

**Q.**Calculate the thermal efficiency of a Carnot's heat engine working between ice point and steam point.

- 26.81%
- 12.97%
- 33.33%
- 83.19%

**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.

- 0.6
- 0.75
- 0.8
- 0.4

**Q.**Find the efficiency of the thermodynamic cycle shown in figure for an ideal diatomic gas.

- 14
- 19
- 18
- 118

**Q.**

Determine the time taken by a 500 W heater to raise the temperature of 50 kg of material of specific heat capacity $920\mathrm{J}.{\mathrm{kg}}^{-1}.{\mathrm{K}}^{-1}$, from ${18}^{\circ}\mathrm{C}$ to ${38}^{\circ}\mathrm{C}$. Assume that all the heat supplied by the heater is given to the material.

**Q.**Two vessels of the same volume contain the same ideal gas at the same temperature. If the pressure in the vessels are in the ratio of 1 : 2, then

- The ratio of the average kinetic energies is 1 : 2
- The ratio of the root mean square velocities is 1 : 1
- The ratio of the average velocities is 1 : 2
- The ratio of the number of molecules is 1 : 2

**Q.**An ideal gas changes state as shown in the figure. What is the work done by the gas in the process?

- Infinite
- Zero
- Negative
- Positive

**Q.**The heat rejected per cycle by a heat engine to the surroundings is 60 % of the heat supplied. Find the efficiency of heat engine.

- 60%
- 40%
- 20%
- 75%

**Q.**

Are heat engines reversible?