Question 11 Mark
Is it possible to liquefy a gas at any condition?
Answer
View full question & answer→No, beyond critical temperature, it is not possible to liquefy however large the pressure may be.
Questions · Page 1 of 2
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Question 21 Mark
How much will be the internal energy change in:
- Isothermal process.
- Adiabatic process?
Answer
View full question & answer→- Zero.
- nCvdT.
Question 31 Mark
Work depends on path in a thermodynamical process. How?
Answer
View full question & answer→Depending on the process carried out, the work done varies. So, it is dependent on path.
Question 41 Mark
What type of process is a Carnot cycle?
Answer
View full question & answer→Carnot cycle is a reversible cyclic process through which heat is converted into mechanical work.
Question 51 Mark
Put a piece of chalk into water. The chalk will emit bubbles in all directions. Explain.
Answer
View full question & answer→The perforations in it will get filled with water and the air is released as bubble.
Question 61 Mark
Change in internal energy is independent of path followed. Is it true? Why?
Answer
View full question & answer→Yes, change in internal energy depends on the change in temperature alone. So, it is independent of path.
Question 71 Mark
A piece of lead is hammered. Does its internal energy increase? Does the heat enter the lead from outside?
Answer
View full question & answer→Yes, internal energy of lead increases. No heat energy from outside enters the lead.
Question 81 Mark
What is the nature of P-V diagram for isobaric and isochoric processes?
Answer
View full question & answer→The P-V diagram for an isobaric process is a straight line parallel to volume axis while that for an isochoric process, it is a straight line parallel to pressure axis.
Question 91 Mark
If on giving 40J of heat to a system, work done on the system is 10J. What will be the change in internal energy of the system?
Answer
View full question & answer→Internal energy of the system will increase by 40 + 10 = 50 joule.
Question 101 Mark
The coefficient of performance of a refrigerator depends on which factor?
Answer
View full question & answer→The coefficient of performance of a refrigerator depends on the temperatures of source and sink.
Question 111 Mark
Can the temperature of a system be increased without heating it?
Answer
View full question & answer→Yes, for example in adiabatic compression.
Question 121 Mark
Why can a Carnot's engine not get 100% efficiency?
Answer
View full question & answer→Due to transmission loss, the energy required to carry the process itself and the inability to build a sink at zero kelvin, one cannot get 100% efficient Carnot's engine.
Question 131 Mark
Why a gas is cooled when it expand?
Answer
View full question & answer→When a gas expands, it does work on the surroundings. This work is done on the expense of internal energy and that is why its internal energy and so its temperature decreases.
Question 141 Mark
Can two isothermal curves intersect? Why?
Answer
View full question & answer→No, since then for two different sets of physical parameters the system may be identified, leading to different states.
Question 151 Mark
What are the forces which make any process irreversible?
Answer
View full question & answer→All sorts of dissipative forces, e.g. force of friction, viscous drag, electrical resistance, non-elasticity, thermal radiation, convection etc., make a real process irreversible.
Question 161 Mark
What does the flat portion in an isotherm indicate?
Answer
View full question & answer→Flat portion refers to the transition from gas to liquid as the gas is compressed. As temperature increases, the flat portion's size reduces.
Question 171 Mark
What is the value of specific heat of water in S.I. units? Does it vary with temperature?
Answer
View full question & answer→Specific heat of water is 4180J kg-1K-1. Yes, it does vary little with temperature.
Question 181 Mark
Heat is being supplied to a system but the system does not perform any external work. Is it possible? If yes, how?
Answer
View full question & answer→Yes, it is possible. If total quantity of heat $\Delta\text{Q}$ supplied to a system is retained by it as its increase in internal energy $\Delta\text{U}$ i.e., $\Delta\text{Q}-\Delta\text{U,}$ then the external work done by the system AW is zero. Isochoric process is an example of this type of process.
Question 191 Mark
In summer, when the valve of a bicycle tube is removed, the escaping air appears cold. Why?
Answer
View full question & answer→This happens due to adiabatic expansion of the air of the tube of the bicycle.
Question 201 Mark
Find the values of two molar specific heats of nitrogen. Given, $\gamma=1.41$ and R = 8.31J mol-1K-1.
Answer
View full question & answer→Given, R = 8.31J mol-1K-1 and $\gamma=1.41$
We know, $\text{C}_\text{V}=\frac{\text{R}}{(\gamma-1)}=\frac{8.31}{(1.41-1)}$
$=20.3\text{J mol}^{-1}\text{K}^{-1}$
$\because\frac{\text{C}_\text{p}}{\text{C}_\text{V}}=\gamma$
$\Rightarrow\text{C}_\text{p}=\text{C}_\text{v}.\gamma$
$=20.3\times1.41=28.263\text{J/mol}-\text{K}$
We know, $\text{C}_\text{V}=\frac{\text{R}}{(\gamma-1)}=\frac{8.31}{(1.41-1)}$
$=20.3\text{J mol}^{-1}\text{K}^{-1}$
$\because\frac{\text{C}_\text{p}}{\text{C}_\text{V}}=\gamma$
$\Rightarrow\text{C}_\text{p}=\text{C}_\text{v}.\gamma$
$=20.3\times1.41=28.263\text{J/mol}-\text{K}$
Question 211 Mark
Two isothermal curves do not intersect each other, why?
Answer
View full question & answer→If two isothermal curves intersect, this implies that the pressure and volume of a gas are the same at two different temperatures, that's impossible.
Question 221 Mark
A system goes from P to Q by two different paths in the P-V diagram as shown in Fig. Heat given to the system in path 1 is 1000J. The work done by the system along path 1 is more than path 2 by 100J. What is the heat exchanged by the system in path 2?
Answer
View full question & answer→For path (1) Q1 = +1000J
W.D =W1 - W2=100
W1 = WD through path 1
W2 = WD through path 2
$\therefore$ W2 = W1 - 100 As change in internal energy by path 1 and 2 are same
$\Delta\text{U}=\text{Q}_{1}-\text{W}_{1}=\text{Q}_{2}-\text{W}_{2}$
1000 - W1 = Q2 - (W1 - 100)
1000 = Q2 + 100
Q2 = 900J.
W.D =W1 - W2=100
W1 = WD through path 1
W2 = WD through path 2
$\therefore$ W2 = W1 - 100 As change in internal energy by path 1 and 2 are same
$\Delta\text{U}=\text{Q}_{1}-\text{W}_{1}=\text{Q}_{2}-\text{W}_{2}$
1000 - W1 = Q2 - (W1 - 100)
1000 = Q2 + 100
Q2 = 900J.
Question 231 Mark
State Carnot's principle.
Answer
View full question & answer→No engine working between two temperatures can be more efficient than a Carnot's reversible engine working between the same temperatures.
Question 241 Mark
Write conditions for an isothermal process.
Answer
View full question & answer→The conditions for an isothermal process are:
- The walls should be diathermic.
- The process should be quasi-static.
Question 251 Mark
What is the change in internal energy of an ideal gas which is compressed/ expanded isothermally? Why?
Answer
View full question & answer→Zero, because for an ideal gas internal energy is wholly kinetic and it is a function of temperature. As temperature remains constant in an isothermal process, hence, internal energy of an ideal gas remains constant.
Question 261 Mark
What is the temperature at the bottom of a lake when water gets frozen with -ve temperature in the atmosphere?
Answer
View full question & answer→It can go down only upto 4°C.
Question 271 Mark
Is it possible to convert internal energy into work or mechanical energy?
Answer
View full question & answer→Yes, for example in an adiabatic expansion and explosion of a bomb (chemical energy is converted into K.E.).
Question 281 Mark
What is the thermodynamical work in a reversible process?
Answer
View full question & answer→Zero.
Question 291 Mark
When a bottle of cold carbonated drink is opened, a slight fog is formed around the opening, why?
Answer
View full question & answer→In opening of bottle, adiabatic expansion of gas causes lowering of temperature.
Question 301 Mark
Three stars A, B, C appear as green, red and blue respectively. Which star has minimum temperature?
Answer
View full question & answer→As $\text{T}\propto\frac{1}{\lambda_\text{m}}$ and $\lambda_\text{m}$ for red colour is maximum, therefore temperature T is minimum for star B emitting red colour.
Question 311 Mark
If a gas is suddenly compressed, its temperature increases, why?
Answer
View full question & answer→Because sudden compression of a gas is an adiabatic process. According to the first law of thermodynamics,
$\Delta\text{Q}=\Delta\text{U}+\Delta\text{W}$
$\because\Delta\text{Q}=0$
$\therefore\Delta\text{U}=-\Delta\text{W}$
$\because\Delta\text{W}=$ negative because work done on the gas
Thus, $\Delta\text{U}$ increases and gas temperature rises.
$\Delta\text{Q}=\Delta\text{U}+\Delta\text{W}$
$\because\Delta\text{Q}=0$
$\therefore\Delta\text{U}=-\Delta\text{W}$
$\because\Delta\text{W}=$ negative because work done on the gas
Thus, $\Delta\text{U}$ increases and gas temperature rises.
Question 321 Mark
Find the efficiency of the Carnot engine working between boiling point and freezing point of water.
Answer
View full question & answer→Efficiency of Carnot engine, $\eta=1-\frac{\text{T}_2}{\text{T}_1}$
$=1-\frac{273\text{K}}{373\text{K}}=\frac{100}{373}$
$=0.268=26.8\%$
$=1-\frac{273\text{K}}{373\text{K}}=\frac{100}{373}$
$=0.268=26.8\%$
Question 331 Mark
What is the efficiency of a Carnot engine operating between boiling and freezing points of water?
Answer
View full question & answer→$\eta=1-\frac{\text{T}_2}{\text{T}_1}$
$=1-\frac{273}{273}=0.27$
$=1-\frac{273}{273}=0.27$
Question 341 Mark
Apply first law of thermodynamics for isothermal expansion of an ideal gas.
Answer
View full question & answer→First law of thermodynamics gives, $\Delta\text{Q}=\Delta\text{U}+\Delta\text{W}$
For an isothermal expansion, $\Delta\text{U}=0$
So, $\Delta\text{Q}=\Delta\text{W}$
For an isothermal expansion of the ideal gas work done by the gas is equal to the heat given to the ideal gas.
For an isothermal expansion, $\Delta\text{U}=0$
So, $\Delta\text{Q}=\Delta\text{W}$
For an isothermal expansion of the ideal gas work done by the gas is equal to the heat given to the ideal gas.
Question 351 Mark
What is the value of $\gamma$ for a gas having 'n' degrees of freedom?
Answer
View full question & answer→For n degrees of freedom,
$\text{C}_\text{v}=\frac{\text{n}}{2}\text{R},\text{C}_\text{P}=\Big(\frac{\text{n}}{2}+1\Big)\text{R}$
$\therefore\gamma=\frac{\text{C}_\text{P}}{\text{C}_\text{V}}=\frac{\frac{\text{n}}{2}+1}{\frac{\text{n}}{2}}=\frac{2+\text{n}}{\text{n}}$
$\text{C}_\text{v}=\frac{\text{n}}{2}\text{R},\text{C}_\text{P}=\Big(\frac{\text{n}}{2}+1\Big)\text{R}$
$\therefore\gamma=\frac{\text{C}_\text{P}}{\text{C}_\text{V}}=\frac{\frac{\text{n}}{2}+1}{\frac{\text{n}}{2}}=\frac{2+\text{n}}{\text{n}}$
Question 361 Mark
Is first law a conservation law? How?
Answer
View full question & answer→Yes, the total heat energy change is the sum of the internal energy change and work done.
$\Delta\text{Q}=\Delta\text{U}+\Delta\text{W}.$
$\Delta\text{Q}=\Delta\text{U}+\Delta\text{W}.$
Question 371 Mark
A piece of lead is hammered. Does its internal energy increase? Does the heat enter the lead from outside?
Answer
View full question & answer→Yes, internal energy of lead increases. No heat energy from outside enters the lead.
Question 381 Mark
At what temperature do the Celsius and Fahrenheit scales coincide?
Answer
View full question & answer→-40°C.
Question 391 Mark
On what factors, the efficiency of a Carnot engine depends?
Answer
View full question & answer→The efficiency of a carnot engine depends on the temperature of source of heat and the sink.
Question 401 Mark
At what temperature do the Kelvin and Celsius scales coincide?
Answer
View full question & answer→Kelvin and Celsius scales never coincide.
Question 411 Mark
Can we decide whether change in internal energy of a system is due to heating or performance of work?
Answer
View full question & answer→No, as internal energy might change due to both heating and performance of work.
Question 421 Mark
Is reversible process possible in nature?
Answer
View full question & answer→A reversible process is never possible in nature because of dissipative forces and condition for a quasi-static process is not practically possible.
Question 431 Mark
Why can an engine working under isothermal conditions produce no useful work?
Answer
View full question & answer→We know that $\eta=1-\frac{\text{T}_2}{\text{T}_1}$
For isothermal operation of the engine, $\text{T}_1=\text{T}_2$
So, $\eta=0$
Hence an engine working under isothermal condition can do no useful work.
For isothermal operation of the engine, $\text{T}_1=\text{T}_2$
So, $\eta=0$
Hence an engine working under isothermal condition can do no useful work.
Question 441 Mark
Cp is greater than Cv why?
Answer
View full question & answer→Cp is greater since under constant pressure process, the energy also does work.
Question 451 Mark
Which one among a solid, liquid and gas of the same mass and at the same temperature has the greatest internal energy and which one has the least?
Answer
View full question & answer→A gas has greatest internal energy and a solid has the least internal energy.
Question 461 Mark
If the temperature of the sink is increased, what will happen to the efficiency of Carnot engine?
Answer
View full question & answer→Efficiency, $\eta=1-\frac{\text{T}_1}{\text{T}_2}$
By increasing (T2), the efficiency of the Carnot engine will decrease.
By increasing (T2), the efficiency of the Carnot engine will decrease.
Question 471 Mark
Which thermodynamic law put restrictions on the complete conversion of heat into work?
Answer
View full question & answer→According to second law of thermodynamics, heat energy cannot converted into work completely.
Question 481 Mark
Is coefficient of performance of a refrigerator constant?
Answer
View full question & answer→No, the coefficient of performance of refrigerator decreases with decrease in its inside temperature.
Question 491 Mark
What is the specific heat of a gas in an isothermal process and in an adiabatic process?
Answer
View full question & answer→Since $\text{s}=\frac{\text{Q}}{\text{m}\Delta\text{t}}$
For isothermal process, $\text{s}=\infty(\because\Delta\text{t}=0)$
For adiabatic process, $\text{s}=0.(\because\Delta\text{Q}=0)$
For isothermal process, $\text{s}=\infty(\because\Delta\text{t}=0)$
For adiabatic process, $\text{s}=0.(\because\Delta\text{Q}=0)$
Question 501 Mark
Why does a gas get heated on compression?
Answer
View full question & answer→Because work done in compressing the gas increases the internal energy of the gas.