NCERT Solutions Class 11 Physics Chapter 11 Thermodynamics

Here, we have offered the NCERT books solutions for all the questions of the Class 11 Physics Chapter 11 Thermodynamics. There are step-by-step solutions.

Q.12.1 A geyser heats water flowing at the rate of 3.0 liters per minute from 27 °C to 77 °C. If the geyser operates on a gas burner, what is the rate of consumption of the fuel if its heat of combustion is 4.0 ×  ${10}^4$ J/g?

Ans.12.1 Initial temperature,  $T_1$ = 27 °C

Final temperature,  $T_2$ = 77 °C

Rise in temperature,  $∆T=T_2-T_1=50℃$

Heat of combustion = 4.0 ×  ${10}^4$ J/g

Specific heat of water, c = 4.21 J/g/  $℃$

Mass of flowing water, m = 3 lit/min = 3000 g/min

Total heat used,  $∆Q=mc∆T$ = 3000  $\times 4.21\times 50$ = 6.315  $\times {10}^5$ J/min

Rate of consumption =  $\frac{6.315\mathrm{}\times {10}^5}{4.0\mathrm{}\times \mathrm{}{10}^4}$ g/min = 15.79 g/min

Ans.12.2 Mass of Nitrogen, m = 2.0 ×  ${10}^{-2}$ kg = 20 g

Rise in temperature,  $∆T$ = 45 °C

Molecular mass of  $N_2$ . M = 28

Universal gas constant, R = 8.3 J mol–1 K–1

Number of moles, n =  $\frac{m}{M}$ =  $\frac{20}{28}$ = 0.714

Molar specific heat at constant pressure for nitrogen,  $C_p$ =  $\frac{7}{2}$ R = 29.05 J/mol/K

The total amount of heat to be supplied is given by the relation

$∆$ Q = n  $C_p∆T$ = 0.714  $\times 29.05\times 45$ = 933.38 J

Q.12.3 Explain why

(a) Two bodies at different temperatures T1 and T2 if brought in thermal contact do not necessarily settle to the mean temperature (T1 + T2 )/2.

(b) 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.

(c) Air pressure in a car tyre increases during driving.

(d) The climate of a harbor town is more temperate than that of a town in a desert at the same latitude.

Ans.12.3

(a) When the two bodies at different temperatures brought in contact, heat flows from the body of higher temperature to the body with lower temperature till the thermal equilibrium is achieved and both the body attains the temperature of (T1 + T2 )/2. But only when the thermal capacities of both the bodies are equal.

(b) The coolant used in Chemical or in Nuclear plant should have high specific heat. Higher specific heat allows coolant to absorb more heat.

(c) In motion, the air temperature inside the tyre increases due to the motion of the air molecules. According to Charles’s law, temperature is directly proportional to pressure. Hence, the air pressure inside the tyre also increases.

(d) A harbor town has a temperate climate ( without extreme heat or cold) than a town located in a desert at the same latitude. This is because the relative humidity in a harbor town is more than it is in a desert town.

Ans.12.4 The cylinder is completely insulated from its surroundings. As a result, no heat is exchanged between the system (cylinder) and its surroundings. Thus the process is ‘Adiabatic’.

Let the initial and final pressure inside the cylinder be  $P_1$ &  $P_2$ and volume be  $V_1$ &  $V_2$ .

Ratio of specific heat,  $\gamma$ = 1.4

For an adiabatic process, we know  $P_1{V}_1^{\gamma }$ =  $P_2{V}_2^{\gamma }$

It is given  $V_2=$  $\frac{V_1}{2}$

Hence  $P_1{V}_1^{\gamma }$ =  $P_2{\frac{V_1}{2}}^{\gamma }$ or  $\frac{P_2}{P_1}$ = (  $V_1^{\gamma })/$ (  ${\frac{V_1}{2}}^{\gamma })$ =  $2^{\gamma }$ =  $2^{1.4}$ = 2.639

Hence the pressure increases by a factor of 2.639