Thermodynamics Questions and Answers

0 At constant pressure when a monatomic ideal gas is heated from temperature T to T it does 40 J of work The heat supplied to the gas during this process is 1 40 J 2 60 J 4 100 J 3 80 J

Which statement is incorrect All reversible cycles have same efficiency 2 Reversible cycle has more efficiency than an irreversible one 3 Carnot cycle is a reversible one 4 Carnot cycle has the maximum efficiency in all cycles Corret

A monoatomic gas at a pressure P having a volume V expands isothermally to a volume 2V and then adiabatically to a volume 16V the final pressure of the gas is take y 5 3 AIPMT 2014 1 64P 3 P 64 2 32P 4 16P

100 An ideal gas undergoes a circular cycle centered at 4 atm 4 lit as shown in the diagram The maximum temperature attained in this process is closed to a 30 R 6 36 R c 24 R d 16 R P atm 6 4 2 t 246 V lit

1 20 joule 2 30 joule 3 30 joule During an adiabatic process the pressure of a gas is found to be proportional to the cube of its absolute temperature The value of y for the gas is 1 3 2 75 4 from 927 C to 27 C is

Two samples of a gas A and B initially at same temperature and pressure are compressed to half their initial volume A isothermally and B adiabatically The final pressure in 1 A and B will be same 2 A will be more than in B 3 A will be less than in B 4 A will be double that in B 199 msso boot required to raise the temperature of 100 gm water from 20 C to 40 C will be

In a sealed vessel of constant volume diatomic gas is present Due to significant increase in temperature certain molecules dissociated into atoms as a result of which specific heat capacity of gas decreased by 8 What fraction of moles got dissociated fed adidas a ffe faud hakarya fara 144 vir die 4 40 34 a

88 For the p V diagram shown for path 1 2 3 100 J of heat is given to the system and 40 J of work is done by the system For path 1 4 3 the work done by system is 10 J Then PA 1 a U3 U 60 J b For 31 the heat is rejected and equal to 85 J c For 1 4 the work done by system is 10 J d For 1 4 the heat given to system is 20 J

An equimolar mixture of a mono atomic and diatomic gas is subjected to continuous expansion such that dQ 1 au aw The equation of the process in terms of the variable P V will be A Pys 4 cons tan B Py11 8 cons tan C Py8 3 cons tan D nu9 4

11 Three samples of the same gas A B and C y 3 2 have initially equal volumes Now the volume of each sample is doubled The process is adiabatic for A isobaric for B and isothermal for C If the final pressures are equal for all three samples the ratio of their initial pressures are a 2 2 2 1 c 2 1 2 b 2 2 1 2 d 2 1 2

The amount of heat given to the gas is equal to the decrease in its internal energy and the work done by the gas is 2 times heat given If y ratio of specific heats is given then the equation of process would 2 y x 3 X K The value of x in the be PV equation is P pressure V volume K constant

27 One mole of an ideal gas undergoes a process Po p Here po and Vo are constants 19 V 1 Change in temperature of the gas when volume is changed from V Vo to V 2V is b ITROVO 10R d povo 2povo a 2000 5R 5 povo AR 2 c

An adiabatic cylinder has 8 gm of helium A light smooth adiabatic piston is connected to a light spring of force constant 30 N m The other end of the spring is connected with a block of mass 1 kg kept on a rough horizontal surface of coefficient of friction 0 3 Area of cross section of cylinder is a 25 cm Initially the spring is in a relax position and the temperature of the gas is 400 K The gas heated slowly from some time by means of an electric heater so as the block M just start moving If work done by the gas is W in J then the value of 10W is 11 3 M

The molar heat capacity in a process of a Q diatomic gas if it does a work of 4 when a heat of Q is supplied to it is Question Type Single Correct Type 1 R 2 5 2 512

Q 34 One kg of air is heated in a closed vessel i e at a constant volume from a pressure of 2 bar to 5 bar If the initial temperature of the air is 300 K determine the change in internal energy c 0 712 kJ kg K 220 4 kJ 120 4 kJ

Q 32 A volume of 0 5 m of gas at a pressure of 10 bar and 200 C is expanded in a cylinder to 1 2 m at a constant pressure Calculate the amount of work done by the gas and the increase in internal energy Assume Cp 1 005 kJ kg K and c 0 712 kJ kg K 500 kJ and 1797 kJ 200 kJ and 1597 kJ O900 kJ and 1497 kJ 700 kJ and 1697 kJ

2P 2 One mole of an ideal monoatomic gas is taken along a cyclic process take 3 14 P Po 3 12 3 V Vo 2V0 Process 1 2 One fourth of the circle Process 2 3 Isochoric Process 3 1 Isobaric

For a heat engine performing between the temperature 273 K and 409 5 K which among the following cannot be the efficiency 15 2

In a certain process PVX Constant the heat Q given to a monoatomic gas leads to a change in internal energy of a Q 4 gas which is equal to 79 2 The value of x is

A ideal gas does 8 J of work during an adiabatic process If its temperature decreases by 4 K then the change in internal energy of the gas will be 16 J 10 J 2 J 8 J

A bullet is fired horizontally down an open cylinder of cross sectional area 10 m When the gun is fired bullet is at rest and the volume between the end of cylinder and bullet is 5 x 10 m and pressure of gas in this volume is 8P where P is atmospheric pressure Gaseous mixture in the cylinder has y 1 5 The bullet moves down quickly so that no heat is transferred to the gas Friction between bullet and the barrel is negligible and no gas leaks around bullet P 10 N m Closed End Open End Bullet

A B C D its volume and a similar specimen in the second vessel is expanded adiabatically the same extent then In the second vessel both pressure and work done are more In the second vessel pressure in more but the work done is less In the first vessel both pressure work done are more In the first vessel pressure is more but work done is less

According to answer key option 4 is orrect but my answer is 600R 2 A monoatomic ideal gas undergoes an adiabatic process from temperature 300 K to 600 K The gas has 2 moles calculate work done by this ideal gas NCERT Pg 3121 w 3124 2 200 R J 1 600 R J Y 3 450 R J 4 900 R J

36 The efficiency of a Carnot cycle is 1 6 By lowering the temperature of sink by 65 K it increases to 1 3 The initial and final temperatures of the sink are 1 390 K and 325 K 3 350 K and 275 K 37 Find the work done by 2 450 K and 410 K 4 400 K and 310 K the gas in the process

Q1A blower handles 1 kg s of air at 20 C and consumes a power of 15 kW The inlet and outlet velocities of air are 100 m s and 150 m s respectively Find the exit air temperature assuming adiabatic conditions Take cp of air is 1005 KVka K We

In the indicator diagram as shown in the following figure the work done along path AB will be C Pressure in Nm 40 30 20 10 1 O 45 J O 90 J O 30 J Zero 2 3 Volume in m B

One mole of an ideal gas having volume 100 cc pressure 1 atm and temperature 100 C undergoes a cyclic process The net internal energy change in one cycle is O Zero O 40 J O 10 J O Insufficient information

5 3 200 K 4 250 K 600 J of heat is added to a monoatomic gas in a process in which the gas performs a work of 150J The molar heat capacity for the process is 1 3R 2 4R 32R 4 6R 16 3 La ETT 1

The ratio of rms speed and most probable speed of molecules of an ideal gas is R at temperature T If the temperature is increased by 2 then the percentage change in the ratio will be O 2 O 4 O 3

eversi Let AW be the work done in quasi static thermodynamic process Which of the following statements about AW is correct a AW is a perfect differential if the process is isothermal b AW is perfect differential if the process is adiabatic c AW is always a perfect differential d AW cannot be a perfect differential

The work done by a gas taken through the closed process ABCA is O 6Povo O 4Po Vo O Povo Tem

Two ideal Carnot engines operate in Cascade all heat given up by one engine is used by the other engine to produce work between temerature T and T The temperature of the hot reservoir of the first engin is T and the temperature of the cold reservoir of the second engine is T T is temperature of the sink of first engine which is also the source for the second which is also the source for the second engine How is T related to T and T If both engines perform equal amount of work

According to maxwell s distribution of molecular speeds for the below graph for two different samples of gasses A and B at temperature T and T respectively which of the following statements is are incorrect 1 dN N dV Gas A 7 Gas B T as V A ifT T then molecular mass of gas B Mg is greater than molecular mass of gas A M B if molecular mass of gas A M is equal to molecular mass of gas B Mg then T T C if T T then molecular mass of gas B M is necessarily less than mass of gas A M Dif gas A is O and gas R is N than considering them to ha 2 ideal gosses than Tis

26 Two rods one made of copper and the other steel of the same length and cross sectional area are joined together The thermal conductivity of copper is 385 J s m K and steel is 50 J s m K If the copper end is held at 100 C and the steel end is held at 0 C what is the junction temperature assuming no other heat losses

4 48 cyclic A refrigerator whose coefficient of performance is 6 extract heat from cooling compartment at the rate of 300 J cycle How much heat per cycle is rejected in the room NCERT Pg 313 1 50 J B 6 2 250 J

94 One mole of an ideal gas at initial temperature T undergoes a quasi static process during which the volume V is doubled During the process the internal energy U obeys the equation U aV where a is a constant The work done during this process is R a 3RT 2 c 5RT 3 A b 5RT 2 d 7RT 3

Consider a monoatomic ideal gas occupying a volume of 22 4 litre at 0 C and 1 atm pressure The work required to compress this gas isothermally to a volume of 16 8 litre is A B 285 J 74 J

A gas takes part in three thermal processes in which it is heated from the same initial state to the same final temperature The process are shown on the P V diagram by straight lines 1 2 1 3 and 1 4 Q Q and Q3 are amount of heat supplied to the gas in the process 1 2 1 3 1 4 respectively Isotherm 16 Q3 Q Q Q Q Q

The volume V of a diatomic gas varies with its temperature T as shown in the graph The ratio of work done by the gas to the heat absorbed by it when it undergoes a change from state A to state B is Question Type Single Correct Type 1 215 4 23

One mole of an ideal gas undergoes a thermodynamic cyclic process as shown in the figure The cyclic process consists of an isochoric an adiabatic process and an isothermal may not be in the same sequence U SPO 3P 2P0 Po V 11 The ratio of molar specific heat at constant pressure to that at constant volume is The ratio of molar specific heat at constant pressure to that at constant volume is Magnitude of work done by the gas in the isothermal process is 2PoVoln 3 2 Magnitude of work done by the gas in the isothermal process is 3P Voln 3 2 B A Vo en3 en3 en2 View in en2 en3 en2

The molar heat capacity at constant volume of oxygen gas at STP is nearly 5R and it approaches 2 7R as the temperature in increased This happens 2 because at higher temperature Question Type Single Correct Type 1 oxygen becomes triatomic 2 oxygen does not behaves as an ideal gas 3 oxygen molecules rotates more vigorously

23 A gas at initial temperature T undergoes sudden expansion from volume V to 2V Then a The process is adiabatic b The process is isothermal c The work done in this process is nRT en 2 where n is the number of moles of the gas d The entropy in the process does not change

and 30 Chis iges Alls 0 0 994 cm 6 A parallel beam of light 2 5890 A is incident on thin glass plate u 1 5 such that the abgle of refraction into the plate is 60 Calculate the smallest thickness of the glass plate which will appear dark by reflection Ans 3 926x10 5 cm

2016 97 The temperature inside a refrigerator is t C and the room temperature is t C The amount of heat delivered to the room for each joule of electrical energy consumed ideally will be atos a b t 273 t t t t 1 t t t 273 1

473 eaction 2062 65 Ink 4 814 T K Enthalpy of the reaction AH at 25 C is 80 kJ 17 12 kJ 34 24 kl L expression for equilibrium constant is given by R 8 3 JK mol

three level system has energies zero E and 2E The level with zero energy is non degenerate v he level with energy E and 2E is doubly and triply degenerate respectively Calculate the mean en of a classical particle in this system at temperature T

The figure shows a frictionless cylindrical piston that seals and floats freely on compressed gas in a cylinder of initial temperature 30 C The temperature is increased to 325 C The factor by which the volume changes is closest to h 1 97 0 51 50 kg 10 8 30 C 10 cm Not enough information to determine

0 If internal energy U of an ideal gas depends on pressure p and volume of the gas according to equation U 3pV which of the following conclusions can you make regarding the gas The gas is not a mono atomic gas b The gas can be a di atomic gas The gas can be a tri atomic gas fe Molar specific heat of the gas in an isobaric process is 4R

Consider a system which has two energy levels one of energy Eo 0 with a degeneracy of two and the other of energy E 1 38 1023 J with a degeneracy of four The partition function at a emperature of 1 K is a 1 47 b 12 87 c 3 47 d 10 87

25 A student in an experimental study of a process 1 2 3 on an ideal ga prepares two graphs to show relations between absolute temperature pressure P and volume V Later he found that he has forgotten to specif a coordinate axis in each graph and marking states in the second graph Unspecified coordinates are shown by letters A and B and unspecifie states by letters x y and z in the second graph Which of the following combinations best suits these graphs a A P B T x 1 y 2 z 3 b A P B T x 3 y 2 z 1 A T B d A T B V x 3 y 2 z 1 T x 1 y 2 z 3