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Question 11 Mark
Explain why :
The climate of a harbour town is more temperate than that of a town in a desert at the same latitude.
Answer
This is because a city near a port has higher humidity values than a desert city.
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Question 21 Mark
Explain why :
The coolant in a chemical or a nuclear plant (i.e., the liquid used to prevent the different parts of a plant from getting too hot) should have high specific heat.
Answer
This is because the heat absorbed by the substance is proportional to the specific heat of the substance. The higher the specific heat, the more heat the coolant will absorb for the same temperature rise
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Question 31 Mark
Write the definition of efficiency of a heat engine.
Answer
The ratio of the mechanical work W provided by some heat and the heat Q taken from the source by the engine is called the efficiency of the engine. This is represent by. Efficiency of heat engine
$\eta=\frac{W}{Q}$
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Question 41 Mark
Give Kelvin-Planck's statement of the second law of thermodynamics.
Answer
According to this statement, no such process is possible, which can completely convert the entire heat taken from a heat reservoir into work
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Question 51 Mark
Explain the meaning of reversible process.
Answer
If in any process, the changes in the external states are applied in the opposite order or opposite direction with respect to the direct process, the same state is obtained at every level, as in the direct process. If this process takes place then it is a reversible process.
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Question 61 Mark
Write two essential properties of an ideal heat engine.
Answer
(i) It should have a source of infinite heat capacity.
(ii) It should have access to an infinite heat capacity.
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Question 71 Mark
In changing the state of a system from A to B does the change in its internal energy depend on the path or not?
Answer
No, because internal energy depends only on the initial and final states and not on the path
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Question 81 Mark
The first law of thermodynamics gives knowledge of the direction in which an action occurs. Is the above statement true or false?
Answer
false
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Question 91 Mark
What is the specific enthalpy of a gas during the adiabatic process?
Answer
For adiabatic process Q = 0
Specific heat $=\frac{Q}{m \Delta T }=0$
Hence, specific heat will be zero.
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Question 101 Mark
What is the specific heat capacity of a gas in isothermal process?
Answer
In isothermal process $\Delta T$ = 0
$\therefore$ Specific heat
$C=\frac{Q}{m \Delta T}=\infty$ hence specific heat capacity will be infinite.
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Question 111 Mark
Why does the pump get hot while filling air in the bicycle tube?
Answer
While filling air in the cycle tube, work done on the air increases the internal energy of the air, due to which the temperature of the air and the pump increases.
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Question 121 Mark
Which change is the solidification of wax?
Answer
Isothermal process, because the temperature remains constant.
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Question 131 Mark
Is superheating of steam an isobaric or isothermal process and why?
Answer
Superheating of steam is an isobaric process, because by continuously giving heat to the steam, the temperature of the steam does not remain constant, rather the temperature increases.
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Question 141 Mark
What is indicator diagram?
Answer
A diagram indicating the diagram of P and V of a body is called indicator diagram.
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Question 151 Mark
Boiling of water at its boiling point is an example of which process?
Answer
Water boils at $100^{\circ}\text C $ at normal pressure, the temperature remains constant in this process. Therefore, boiling of water at its boiling point is an isothermal process.
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Question 161 Mark
How is a heat engine different from a refrigerant?
Answer
It is a heat engine working in the opposite direction from the refrigerator.
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Question 171 Mark
Write Joule's law.
Answer
 According to Joule's law, under proper conditions, work done on a system (W) and heat generated (H) are mutually proportional, that is
$W \propto H \Rightarrow W = JH$
Where J is the mechanical equivalent of heat.
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Question 191 Mark
Write the names of the main parts of Carnot engine.
Answer
(i) Source (ii) Stand (iii) Sink (iv) Working substance.
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Question 201 Mark
When can the efficiency of a frictionless heat engine be 100%?
Answer
When the temperature of the sink is absolute zero or the temperature of the source is infinite. Both of these are impossible.
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Question 211 Mark
State the theorem of functions.
Answer
All those working between two equal temperatures reversible engines have the same efficiency.
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Question 221 Mark
On what factors does the efficiency of a reversible engine depend?
Answer
The efficiency of a reversible engine depends only on the temperature of the source and sink.
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Question 231 Mark
What type of change occurs when a solid melts?
Answer
Melting of a solid is an isothermal change, because when the solid melts, there is no change in its temperature.
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Question 241 Mark
In a isothermal, homogeneous and isobaric processes, in which process is the value of work done for the same volume change more?
Answer
Isobaric process.
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Question 251 Mark
Is it possible that even after heating a body, its temperature does not increase? Does this go against the first law of thermodynamics?
Answer
If all the heat given to the system is converted into work, then its temperature will not increase, that is, it is possible. This is not against the first law of thermodynamics.
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Question 261 Mark
How much value of specific heat of gas in adiabatic change?
Answer
In adiabatic change the value of specific heat of gas is zero, because dQ = 0.
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Question 271 Mark
Which of the solid, liquid and gas kept at the same mass and same temperature will have the maximum internal energy and which will have the minimum?
Answer
Internal energy of gas will be maximum and internal energy of solid will be minimum.
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Question 281 Mark
Can two isotherm curves be intersected each other? Why?
Answer
No, if they intersect each other then the pressure and volume of the gas will be the same for two different temperatures at the intersection point, which is not possible.
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Question 291 Mark
Can the pressure of a gas be changed by keeping both its temperature and volume constant?
Answer
Yes, by changing the quantity of gas.
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Question 301 Mark
Mention the second law of thermodynamics.
Answer
It is impossible to continuously achieve work by continuously obtaining heat from a system and reducing its temperature from the ambient temperature (Kelvin's statement). It is impossible for heat to flow automatically from a system of lower temperature to a system of higher temperature (statement of Clausius).
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Question 311 Mark
What are the necessary conditions for a process to be reversible?
Answer
(i) The change of state in the process should happen very slowly. (ii) The difference between the pressure and temperature of the liquid of the system and the pressure and temperature of the surroundings should not be much. (iii) Heat should not be lost due to friction, viscosity, radiation etc.
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Question 321 Mark
Which working substance is used in reversible Carnot engine?
Answer
In the reversible Carnot engine, ideal gas is used as the working substance.
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Question 331 Mark
What will be the change in internal energy of an ideal gas when it is heated at constant temperature?
Answer
The internal energy of an ideal gas depends only on temperature; hence it has zero. There is no change.
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Question 341 Mark
Which curve has the steepest slope of the P-V diagrams for isothermal and antithermal processes?
Answer
The slope of the post-inhibitory curve is higher.
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Question 351 Mark
Why does an engine work in isothermal conditions can't do gainful work?
Answer
$T_1=T_2$ for isothermal work of engine. Hence, $\eta=0$, hence an engine working in isothermal condition cannot do any profitable work.
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Question 371 Mark
Why can't a ship use the internal energy of sea water to propel it?
Answer
Since there is no access in the ship, so the internal energy of water cannot be used to run the engine.
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Question 381 Mark
What is meant by internal energy?
Answer
The energy due to the movement of molecules in a gas is called internal energy. It is made up of kinetic energy, vibrational energy, rotational energy etc. of molecules.
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Question 391 Mark
Write the formula for the work done to change the volume of one mole of a gas from $V_1$ to $V_2$ in an isothermal process.
Answer
Work done in isothermal process
$ \begin{aligned} W & =RT \log _{e} \frac{V_2}{V_1} \\ & =2.303 P_1 V_1 \log _{10} \frac{V_2}{V_1} \end{aligned} $
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Question 401 Mark
A vessel with adiabatic walls has two chambers. One chamber is filled with gas and the other is a vacuum. The room divider suddenly bursts. What will be the change in the internal energy of the gas in this process?
Answer
Internal energy will remain unchanged.
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Question 411 Mark
A gas expands to a volume of 1 litre at constant pressure $10^5 N / m ^2$. Calculate the work done during this isobaric expansion.
Answer
$ \Delta W=PdV $
[Given that $dV =1$ liter $=10^{-3} m^3$] 
$=10^5 \times 10^{-3}=100$ Joule
Work done $\quad$$\Delta W =100$ Joule
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Question 421 Mark
In which process the heat given to a system is completely converted into work?
Answer
In isothermal process, since dU = 0 in this process.
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Question 431 Mark
Write the first law of thermodynamics.
Answer
The value of heat given to a system is equal to the sum of the change in its internal energy and the work done on it.
$\Delta Q = dU +\Delta W$
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Question 441 Mark
The efficiency of Carnot engine is highest as compared to other heat engines. Is the above statement true or false?
Answer
true
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