Question 1

During a polytropic expansion 25% of heat is converted into work while temperature of gas rises by 30 K, the specific heat of gas at constant volume is&#10;A)10% w&#10;B)12 % w&#10;C)15% w&#10;D)20% w

Accepted Answer

The correct answer is B.Explanation:During a polytropic expansion, the heat converted into work is given by:W = (1 - n) * Qwhere W is the work done, Q is the heat supplied, and n is the polytropic index.The temperature of the gas rises by 30 K, so the heat supplied is given by:Q = m * Cv * dTwhere m is the mass of the gas, Cv is the specific heat at constant volume, and dT is the change in temperature.Substituting these equations into the first equation, we get:W = (1 - n) * m * Cv * dTWe are given that 25% of the heat is converted into work, so:W = 0.25 * QSubstituting this into the previous equation, we get:0.25 * Q = (1 - n) * m * Cv * dTSolving for Cv, we get:Cv = 0.25 * Q / (m * dT * (1 - n))We are given that dT = 30 K and n = 1.2, so:Cv = 0.25 * Q / (m * 30 K * (1 - 1.2))Cv = 0.25 * Q / (m * 30 K * (-0.2))Cv = 0.125 * Q / (m * 30 K)Therefore, the specific heat at constant volume is 12.5% of the heat supplied.

Question 2

During a constant pressure expansion of a gas 33.3 % heat is converted into work while the temperature rises by 20K. The specific heat of gas at constant pressure is&#10;A)10% w&#10;B)12 % w&#10;C)15% w&#10;D)20% w

Accepted Answer

The specific heat at constant pressure (Cp) can be determined using the relation: Cp = (1 - fraction of heat converted to work) * total heat added. Since 33.3% of the heat is converted to work, 66.7% of the heat is used to increase the temperature. Therefore, Cp = 66.7% of the total heat, which corresponds to 15% of the work done (w).

Question 3

During an adiabatic compression when temperature increase by 100% the pressure increases by 1000%. The ratio of specific heats, ? is&#10;A)1.3&#10;B)1.35&#10;C)1.4&#10;D)1.45

Accepted Answer

For an adiabatic process, the relation between pressure (P) and temperature (T) is given by $P \propto T^{\frac{\gamma}{\gamma-1}}$, where $\gamma$ is the ratio of specific heats. Given that temperature increases by 100% (i.e., T becomes 2T) and pressure increases by 1000% (i.e., P becomes 11P), we can write the relation as $11P = (2T)^{\frac{\gamma}{\gamma-1}}$. Simplifying this equation leads to the conclusion that $\gamma = 1.4$, which is characteristic of diatomic gases like nitrogen and oxygen at room temperature.

Question 4

The area under the curve on temperature entropy diagram represents&#10;A)work done during the process&#10;B)heat exchanged during the process&#10;C)change in internal energy during the process&#10;D)change in entropy during the process

Accepted Answer

The area under the curve on a temperature-entropy (T-S) diagram represents the heat exchanged during the process. This is because the heat transfer (Q) is directly proportional to the temperature (T) and the change in entropy (ΔS), as given by the relation Q = TΔS for reversible processes.

Question 5

The change in entropy is zero during&#10;A)hyperbolic process&#10;B)constant pressureprocess&#10;C)adiabatic processes&#10;D)polytropic process

Accepted Answer

In an adiabatic process, there is no heat exchange with the surroundings, which means the entropy change of the system is zero, assuming the process is reversible.

Question 6

Choose incorrect statement&#10;A)isentropic process is adiabatic&#10;B)adiabatic process has no heat exchange&#10;C)hyperbolic process is isothermal&#10;D)no work is done in constant pressure process

Accepted Answer

In a constant pressure process, work is done by the system if there is a change in volume. The statement D is incorrect because work done in a constant pressure process is given by $W = P\Delta V$, where $P$ is the constant pressure and $\Delta V$ is the change in volume. If there is a change in volume, then work is done, contrary to the statement.

Question 7

Choose the correct statement&#10;A)there is no change of entropy in an adiabatic expansion&#10;B)entropy is an extensive property of gas derived from first law of thermodynamics&#10;C)the area under the curve in a temp.-entropy diagram gives the change of entropy&#10;D)the change of entropy during a constant pressure process is always negative

Accepted Answer

Entropy is indeed an extensive property, meaning it depends on the amount of substance present, and it is derived from the second law of thermodynamics, not the first. The first law deals with the conservation of energy, while the second law addresses the direction of thermal processes and the concept of entropy.

Question 8

1.6 Kg of air is expanded at constant pressure from 100°C to 0°C resulting in entropy change of - 2.0 J/K 3.2 Kg of air is cooled at constant volume from 100°C to 0°C with a change in entropy of -3.0 J/K. The ratio Cp/ Cv is

A)1.333
B)1.366
C)1.4
D)1.43

Accepted Answer

The ratio Cp/Cv is the specific heat ratio (γ) for air, which is approximately 1.4 for diatomic gases like air.

Question 9

Entropy at absolute zero temperature is zero for a&#10;A)perfect gas&#10;B)perfect substance&#10;C)perfect crystal&#10;D)glass

Accepted Answer

Entropy at absolute zero temperature is zero for a perfect crystal, according to the third law of thermodynamics. This is because a perfect crystal is in a state of perfect order, with only one possible microstate.

Question 10

The third law of thermodynamics&#10;A)defines entropy&#10;B)provides a base from which entropy is measured&#10;C)defines change of entropy&#10;D)gives availability of heat for conversion into work

Accepted Answer

The answer of The third law of thermodynamics&#10;A)defines entropy&#10;B)provides a...

Question 11

Entropy is called the property of a system because&#10;A)it has same value at any two equilibrium states&#10;B)it depends upon the process path&#10;C)it has a unique value at each equilibrium state&#10;D)it does not change between two equilibriumstates

Accepted Answer

The answer of Entropy is called the property of a...

Question 12

Entropy of mixture of two gases after sudden mixing is&#10;A)greater than&#10;B)less than its inputtemperature&#10;C)same as sum of entropy ofindividual gases&#10;D)unpredictable

Accepted Answer

The answer of Entropy of mixture of two gases after...

Question 13

If a substance goes though a cycle of changes returning back to original state, the change in entropy is&#10;A)positive&#10;B)negative&#10;C)zero&#10;D)positive or negative depending upon originalstate

Accepted Answer

The answer of If a substance goes though a cycle...

Question 14

A sequence of operations which a gas undergoes in such a way that final state is same as original state, mahe a&#10;A)reversible cycle&#10;B)irreversible cycle&#10;C)thermal cycle&#10;D)thermodynamic cycle

Accepted Answer

The answer of A sequence of operations which a gas...

Question 15

In a reversible process&#10;A)heat transfer takes place over finite temperaturedifference&#10;B)heat transfer takes place over infinitesimaltemperature difference&#10;C)heat transfer takes place from surrounding to thesystem&#10;D)heat transfer takes place from the system tothe surrounding

Accepted Answer

The answer of In a reversible process&#10;A)heat transfer takes place...

Question 16

Which of the following processes is very close to reversible&#10;A)lifting of a body above the ground&#10;B)compression of a gas in the cylinder against a piston&#10;C)flow of a fluid in a pipe&#10;D)motion of a boat in water

Accepted Answer

The answer of Which of the following processes is very...

Question 17

A perfect gas having p1= 0.1 M/mm&#178;, v1=0.18 m&#179;, T1=20&#176;C is compressed to 1/10 of volume in an isothermal process. The change in entropy is&#10;A)-141.45 j/k&#10;B)141.45 j/k&#10;C)-41446.23 j/k&#10;D)0

Accepted Answer

The answer of A perfect gas having p1= 0.1 M/mm&#178;,...

Question 18

The enthalpy of a system&#10;A)i= internal energy + pv&#10;B)i= internal energy + pdv&#10;C)i= internal energy + vdp&#10;D)i= change in internalenergy + pv

Accepted Answer

The answer of The enthalpy of a system&#10;A)i= internal energy...

Question 19

Which statement is wrong for throttling expansion&#10;A)pressure drop = 0&#10;B)change in enthalpy = 0&#10;C)work done = 0&#10;D)change in internalenergy = 0

Accepted Answer

The answer of Which statement is wrong for throttling expansion&#10;A)pressure...

Question 20

Which statement is wrong for adiabatic expansion&#10;A)h = 0&#10;B)w = 0&#10;C)ds = 0&#10;D)w+e = 0

Accepted Answer

The answer of Which statement is wrong for adiabatic expansion&#10;A)h...

Question 21

Maximum amount of work that can be converted into heat in any process&#10;A)depends upon initial & final temperature&#10;B)depends upon how much work is lost in friction&#10;C)is 50%&#10;D)is 100%

Accepted Answer

The answer of Maximum amount of work that can be...

Question 22

The universal gas constant will be equal to difference between specific heats at constant pressure & constant volume for&#10;A)1 kg mass of gas&#10;B)1 molecule of gas&#10;C)1 kg molecule of gas&#10;D)any mass of gas

Accepted Answer

The answer of The universal gas constant will be equal...

Question 23

Air is compressed isothermally by performing work equal to 16 KJ upon it. The change in internal energy is&#10;A)- 16 kj&#10;B)zeroth law of thermodynamics&#10;C)16 kj&#10;D)32 kj

Accepted Answer

The answer of Air is compressed isothermally by performing work...

Deck 7: Thermodynamics