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Q1. Which word is defined by this statement: A measure of the disorder, or randomness?

• energy
• entropy
• enthalpy
• mass

Solution

Entropy is the measure of disorder or randomness.

Q2. Two identical blocks of iron, one at 10^oC and the other at 20^oC, are put in contact. Suppose the cooler block cools to 5^oC and the warmer block warms to 25^oC. This would violate the

• First Law of Thermodynamics
• Gauss law
• Zeroth Law of Thermodynamics
• Second Law of Thermodynamics

Solution

Second Law of Thermodynamics

Q3. Three samples A, B and C of same gas initially having same volume and pressure are expanded to double their initial volume. One sample A is expanded isothermally, B is expanded adiabatically and C is expanded isobarically. In which case is the work done minimum?

• In isothermal expansion
• In adiabatic expansion
• In isochoric expansion
• Work done in all cases is same

Solution

The minimum work is done in case of adiabatic expansion.

Q4. Which of the following are the extensive variables?

• Internal energy, volume, total mass
• Pressure, temperature and density
• Internal energy, pressure and volume
• Pressure, temperature and volume

Solution

Internal energy, volume, total mass are extensive variables. Pressure, temperature, etc are intensive variables.

Q5. Find the final temperature of one mole of an ideal gas which has an initial temperature t K. The gas does 9 R joules of work adiabatically. The ratio of specific heats of this gas at constant pressure and at constant volume is 4/3.

• (t-9)K
• (t+3) K
• (t-3) K
• (t-4/3) K

Solution

T_Initial  = t K Work, W = 9R Ratio of specific heats, γ = C_p / C_v = 4/3 In an adiabatic process, we have W = R(T_Final – T_initial) / (1-γ) 9R = R (T_Final – t) / (1 – 4/3) T_Final – t = 9 (-1/3) = -3 T_Final  = (t-3) K

Q6. In a Carnot engine 800 J of heat is absorbed from a source at 400 K and 640 J of heat is rejected to the sink. The temperature of the sink is:

• 320 K
• 100 K
• 273 K
• 250 K

Solution

Q7. In actual home refrigerator vapours of Freon ( which is dichlorodifluoro methane CCl₂F₂) act as

• Source
• Sink
• Working substance
• Insulating pad

Solution

In actual home refrigerator vapours of Freon ( which is dichlorodifluoro methane CCl₂F₂) act as working substance.

Q8. Which of the following is not a reversible process?

• An ideal gas allowed to expand slowly and the compressed slowly so as to reach its initial state
• Rusting of iron
• Slow compression and extension in a spring
• Electrolysis process where resistance offered by electrolyte is zero

Solution

Rusting of iron is not a reversible process.

Q9. The second law of thermodynamics says

• Efficiency of a heat engine can be 100%.
• Coefficient of performance can never be infinite for refrigerator
• Heat released to the cold reservoir can be zero
• Ideal gas can expand infinitely

Solution

The second law of thermodynamics says coefficient of performance can never be infinite for refrigerator.

Q10. Heat is supplied to the gas, but its internal energy does not increase. What is the process involved?

• Isochoric process
• Isothermal process
• Isobaric process
• None of the above

Solution

The process involved is isothermal expansion.

Q11. The internal energy and the work done by a system decreases by same amount then

• The temperature must decrease
• The process must be adiabatic
• The process must be isothermal
• a and b both

Solution

Loss in internal energy = work done by the system, dQ = 0, therefore process is adiabatic. Loss in internal energy shows there would be a decrease in temperature.

Q12. The first law of thermodynamics 1. Is a restatement of the principle of conservation of energy as applied to heat energy 2. Is the basis for the definition of internal energy 3. Is basis for the definition of temperature 4. asserts the impossibility of achieving an absolute zero temperature.

• Both 1 and 2
• Only 1
• Both 1 and 3
• 1,2,4

Solution

Both 1 and 2

Q13. What are the four stages of Carnot cycle?

• Isothermal expansion, adiabatic expansion, isothermal compression, adiabatic compression
• Isothermal compression, isochoric expansion, isothermal expansion, adiabatic compression
• Isothermal expansion, adiabatic expansion, isochoric compression, isothermal compression
• Isothermal compression, isochoric expansion, isothermal expansion, isochoric compression

Solution

Isothermal expansion, adiabatic expansion, isothermal compression, adiabatic compression.

Q14. Hot coffee in a thermos flask is shaken vigorously, considering it as a system which of the statement is not true?

• Work is done on the system
• Temperature of the system rises
• Heat energy has been added to coffee
• Internal energy of the coffee increased

Solution

As thermos flask is insulated, so no heat is added to the system. Hence, ∆Q = 0. Work is done on the system by shaking it against viscous force. Hence, ∆w is negative. Temperature of the system rises because of increase in internal energy. Internal energy of coffee ∆U = ∆Q - ∆W = 0 - (-∆W) So, ∆U would be positive.

Q15. According to Carnot theorem no heat engine working between two given temperatures of source and sink can be more efficient than a perfectly ___________ engine working between the same two temperatures

• Ideal gas
• Heat
• Reversible
• Combustible

Solution

According to Carnot theorem no heat engine working between two given temperatures of source and sink can be more efficient than a perfectly Reversible engine working between the same two temperatures.

Q16. If the door of refrigerator is left open inside a closed room, what would happen to the temperature of the room?

• Room temperature would increase
• Room temperature would decrease
• Room temperature would not be effected
• Room temperature would be same as the temperature inside the refrigerator

Solution

If the door of a refrigerator is left open inside a closed room, the temperature of the room would increase. This is because when the door is open, the temperature inside tends to increase. Thus, the motor of the refrigerator starts running and pumps the heat back to the room, thereby increasing the net temperature of the room.

Q17. What is not true for a cyclic process?

• ΔQ = ΔW
• ΔU = 0
• System returns to its initial state
• ΔW= 0

Solution

In a cyclic process system returns to its initial state and ΔU = 0 and the total heat absorbed by the system equals to the work done by the system therefore ΔQ = ΔW.

Q18. Which of the following is an example of heat pump?

• Carnot engine
• Refrigerator
• Blower heater
• Internal combustion engine

Solution

Refrigerator is an example of heat pump.

Q19. The temperature inside a refrigerator is 4^oC and the room temperature is 27^oC. How many joules of heat will be delivered to the room for each joule of electricity consumed by the refrigerator?( Treat the refrigerator as ideal).

• 1 J
• 12 J
• 8.3 J
• 13 J

Solution

Q20. (Molar specific heat capacity at constant pressure) - (Molar specific heat capacity at constant volume) is equal to

• k_B
• R/2
• nR, where n is number of moles
• R

Solution

C_P - C_V = R

Q21. Which one of the following is not an example of the second law of thermodynamics?

• The aerobic respiration of glucose generates heat
• All types of cellular respiration produce ATP
• CO₂ is exhaled as a by-product of aerobic respiration
• Photosynthesis enables plants to create energy from sunlight

Solution

CO₂ is exhaled as a by-product of aerobic respiration is not an example of second law of thermodynamics.

Q22. The First Law of Thermodynamics states that:

• ΔQ -W = ΔU
• ΔQ - ΔU = ΔW
• ΔQ - ΔW = U
• Q -W = U

Solution

The first law of thermodynamics gives ΔQ - ΔU = ΔW

Q23. The Zeroth law leads to the concept of

• heat
• temperature
• internal energy
• work

Solution

The Zeroth law leads to the concept of temperature.

Q24. State the first law of thermodynamics for isochoric process.

• dQ = dW
• dU + dW = 0
• dQ = dU
• dQ = dU + P (V_f - V_i)

Solution

dQ = dU + P (V_f - V_i)

Q25. What amount of work is needed to freeze 1 gm of water at 0˚C in a refrigerator. The temperature of surroundings is 320 K?

• 14.5 cal
• 13.77 cal
• 12.75 cal
• 10 cal

Solution

T₁= 320 K   , T₂= 0˚C= 273K To freeze 1 gm of water at 273 K, 80 cal of heat must be transferred from water at 0˚C to the surroundings. Therefore Q₂= 80 cal The coefficient of performance of refrigerator is given as

Q26. Refrigerator transfers heat from the cold cooling coils to warm surroundings. Which law of thermodynamics favours this process?

• Zeroth law of thermodynamics
• First law of thermodynamics
• Third law of thermodynamics
• Second law of thermodynamics

Solution

In a refrigerator, external work is done by the compressor for the transfer of heat from the cold cooling coils to warm surroundings. Hence, the second law of thermodynamics is not violated and this process is favoured.

Q27. The internal energy of an ideal gas depends on:

• Type of gas
• Pressure
• Volume
• Temperature

Solution

Internal energy of an ideal gas depends only on its internal kinetic energy which in turns depends only on the temperature of the gas.

Q28. Minimum work is said to be done when a gas expands

• Isobarically
• Adiabatically
• Isochorically
• Isothermally

Solution

In an isochoric process  no work is done by or on the system.

Q29. Molar specific heat of a substance denoted by symbol C does not depend upon

• Nature of the substance
• Amount of the substance
• Temperature of the substance
• Condition under which heat is supplied

Solution

Amount of the substance

Q30. Which of the following is not a state variable?

• heat
• temperature
• pressure
• volume

Solution

Heat is not a state variable. The state variables are pressure, volume and temperature.

Q31. In an adiabatic process internal energy of gas

• Increases
• Decreases
• Does not change
• Becomes twice

Solution

In an adiabatic process work done by gas results in decrease in its internal enegy.

Q32. The ratio of quantity of heat removed per cycle from the contents of the refrigerator to the energy spent per cycle to remove this heat is called the

• coefficient of performance
• principle of heat engine
• efficiency of refrigerator
• efficiency of heat engine

Solution

The ratio of quantity of heat removed per cycle from the contents of the refrigerator to the energy spent per cycle to remove this heat is called the coefficient of performance.

Q33. Two gases X and Y kept in separate cylinders with same initial temperature and pressure are compressed to one third of their volume through isothermal and adiabatic process respectively. Which gas would have more pressure?

• Gas X has higher temperature
• Gas Y has higher pressure
• Gas X and Y are at 0 atm pressure
• Gas Y has lower pressure

Solution

Let P₁, P₁' be the initial pressure of the two gases respectively and P₂, P₂' be the final pressure of the two gases. Let V and V/3 be the initial and final volume respectively. In an isothermal compression, we have P₂ = P₁V₁/V₂ = P₁(V/ V/3) = 3P₁ In an adiabatic compression P₂' = P₁' (V₁/V₂)^γ = P₁'(V/ V/3)^γ = P₁ 3^γ                 (as P₁=P₁^’) Since γ >1, therefore P₂' > P₂

Q34. According to the second law of thermodynamics, which of the following is true?

• The total amount of energy in the universe is constant
• Energy conversions increase the order in the universe
• The ordering of one system depends on the disordering of another
• The entropy of the universe is constantly decreasing

Solution

According to the second law of thermodynamics, the ordering of one system depends on the disordering of another.

Q35. Refrigerators X and Y are removing 1000 J of heat from the freezer. Refrigerator X is working between -5^o C and 25^o C and refrigerator Y is working between -20^o C and 20 ^oC. Find efficiency of refrigerator X and Y?

• 8.9, 7.3
• 9.8, 7.3
• 7.9, 6.5
• 20, 2

Solution

Q36. Even Carnot engine cannot give 100% efficiency because we cannot:

• prevent radiation
• find ideal source
• reach absolute zero temperature
• eliminate friction

Solution

Q37. The SI unit of mechanical equivalent of heat is

• KW cal
• erg
• Erg/ calorie
• Joules/ calorie

Solution

SI unit of mechanical equivalent of heat is Joules/ calorie.

Q38. First law of thermodynamics tells us:

• the direction in which a given process can take place
• to what extent the process takes place
• the nature of the process taking place
• that heat supplied is used to carry out the process

Solution

First law of thermodynamics tells that whenever heat is supplied to a system, a part of it increases the internal energy and remaining heat is used in doing external work. Hence, it tells us that heat supplied is used to carry out the process.

Q39. Internal energy of a system increases by 60 J when 140 J of heat is added to the gaseous system. The amount of work done would be:

• 200 J
• 80 J
• 100J
• 140J

Solution

dW = dQ - dU = 140 - 60 = 80 J

Q40. In a heat engine the ratio of net work done per cycle by the engine to the total amount of heat absorbed per cycle by the working substance from the source is known as

• Adiabatic compression ratio
• Specifie heat ratio
• Thermal Efficiency
• Conductivity