Thermodynamics (Physics)

A system is taken from state a to state c by two paths adc and abc as shown in the figure. The internal energy at a is Ua = 10 J. Along the path adc the amount of heat absorbed dQ1 = 50 J and the work obtained dW1 = 20 J whereas along the path abc the heat absorbed dQ2 = 36 J. The amount of work along the path abc is [figure]

1. 10 J
2. 12 J
3. 36 J
4. 6 J

Which of the following relations does not give the equation of an adiabatic process, where terms have their usual meaning?

1. P1- T = constant
2. PV = constant
3. TV -1 = constant
4. P T1- = constant

Two Carnot engines A and B are operated in series. The engine A receives heat from the source at temperature T1 and rejects the heat to the sink at temperature T. The second engine B receives the heat at temperature T and rejects to its sink at temperature T2. For what values of T the efficiencies of the two engines are equal

1. T1 - T22
2. T1T2
3. T1T2
4. T1 + T22

An ideal gas goes from state A to state B via three different processes as indicated in the P-V diagram. [figure] If Q1, Q2, Q3 indicate the heat absorbed by the gas along the three processes and U1, U2, U3 indicate the change in internal energy along the three processes respectively, then

1. Q1 > Q2 > Q3 and U1 = U2 = U3
2. Q3 > Q2 > Q1 and U1 = U2 = U3
3. Q1 = Q2 = Q3 and U1 > U2 > U3
4. Q3 = Q2 = Q1 and U1 > U2 > U3

One mole of an ideal gas goes from an initial state A to final state B via two processes : It first undergoes isothermal expansion from volume V to 3V and then its volume is reduced from 3V to V at constant pressure. The correct P-V diagram representing the two processes is

1. [figure]
2. [figure]
3. [figure]
4. [figure]

A thermodynamic system is taken through the cycle ABCD as shown in figure. Heat rejected by the gas during the cycle is [figure]

1. 2PV
2. 4PV
3. 12PV
4. PV

A mass of diatomic gas ( = 1.4) at a pressure of 2 atmospheres is compressed adiabatically so that its temperature rises from 27 to 927 . The pressure of the gas in the final state is

1. 8 atm
2. 28 atm
3. 68.7 atm
4. 256 atm

During an isothermal expansion, a confined ideal gas does 150 J of work against its surroundings. This implies that

1. 150 J of heat has been removed from the gas
2. 300 J of heat has been added to the gas
3. no heat is transferred because the process is isothermal
4. 150 J of heat has been added to the gas

When 1 kg of ice at 0 melts to water at 0 , the resulting change in its entropy, taking latent heat of ice to be 80 cal/g, is

1. 273 cal/K
2. 8 104 cal/K
3. 80 cal/K
4. 293 cal/K

If cp and cv denote the specific heats (per unit mass) of an ideal gas of molecular weight M, then

1. cp - cv = RM2
2. cp - cv = R
3. cp - cv = RM
4. cp - cv = MR

A monatomic gas at pressure P1 and volume V1 is compressed adiabatically to 18th of its original volume. What is the final pressure of the gas?

1. 64P1
2. P1
3. 16P1
4. 32P1

If and represent the increase in internal energy and work done by the system respectively in a thermodynamical process, which of the following is true?

1. = - , in an adiabatic process
2. = , in an isothermal process
3. = , in an adiabatic process
4. = - , in an isothermal process

The internal energy change in a system that has absorbed 2 kcal of heat and done 500 J of work is

1. 6400 J
2. 5400 J
3. 7900 J
4. 8900 J

In thermodynamic processes which of the following statements is not true ?

1. In an isochoric process pressure remains constant.
2. In an isothermal process the temperature remains constant.
3. In an adiabatic process PV = constant.
4. In an adiabatic process the system is insulated from the surroundings.

If Q, E and W denote respectively the heat added, change in internal energy and the work done in a closed cyclic process, then

1. E = 0
2. Q = 0
3. W = 0
4. Q = W = 0

An engine has an efficiency of 1/6. When the temperature of sink is reduced by 62 , its efficiency is doubled. Temperatures of the source is

1. 37
2. 62
3. 99
4. 124

A Carnot engine whose sink is at 300 K has an efficiency of 40%. By how much should the temperature of source be increased so as to increase its efficiency by 50% of original efficiency?

1. 380 K
2. 275 K
3. 325 K
4. 250 K

The molar specific heat at constant pressure of an ideal gas is (7/2) R. The ratio of specific heat at constant pressure to that at constant volume is

1. 9/7
2. 7/5
3. 8/7
4. 5/7

An ideal gas heat engine operates in Carnot cycle between 227 and 127 . It absorbs 6 104 cal of heat at higher temperature. Amount of heat converted to work is

1. 4.8 104 cal
2. 6 104 cal
3. 2.4 104 cal
4. 1.2 104 cal

Which of the following processes is reversible?

1. Transfer of heat by conduction
2. Transfer of heat by radiation
3. Isothermal compression
4. Electrical heating of a nichrome wire

One mole of an ideal gas at an initial temperature of T K does 6R joule of work adiabatically. If the ratio of specific heats of this gas at constant pressure and at constant volume is 5/3, the final temperature of gas will be

1. (T + 2.4) K
2. (T - 2.4) K
3. (T + 4) K
4. (T - 4) K

An ideal gas heat engine operates in a Carnot cycle between 227 C and 127 C. It absorbs 6 kcal at the higher temperature. The amount of heat (in kcal) converted into work is equal to

1. 4.8
2. 3.5
3. 1.6
4. 1.2

The efficiency of Carnot engine is 50\% and temperature of sink is 500 K. If temperature of source is kept constant and its efficiency raised to 60\%, then the required temperature of sink will be

1. 100 K
2. 600 K
3. 400 K
4. 500 K

A scientist says that the efficiency of his heat engine which works at source temperature 127 and sink temperature 27 is 26\%, then

1. it is impossible
2. it is possible but less probable
3. it is quite probable
4. data are incomplete.

The (W/Q) of a Carnot engine is 16, now the temperature of sink is reduced by 62 , then this ratio becomes twice, therefore the initial temperature of the sink and source are respectively

1. 33 , 67
2. 37 , 99
3. 67 , 33
4. 97 K, 37 K