Thermodynamics (Physics) · Question 30

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