physics ncert solutions class 11th

Ten small planes are flying at a speed of 150 km/h in total darkness in an air space that is 20 * 20 * 1.5 km³ in volume. You are in one of the planes, flying at random within this space with no way of knowing where the other planes are. On the average about how long a time will elapse between near collision with your plane. Assume for this rough computation that a safety region around the plane can be approximated by a sphere of radius 10m.

Consider an ideal gas with the following distribution of speeds

(a) Calculate V_rms and hence T(m=3 $*{10}^{-26}\mathit{k}\mathit{g}$ )

(b) If all the molecules with speed 1000m/s escape from the system , calculate new V_rms and hence T.

Explain why

(a) There is no atmosphere on moon.

(b) There is fall in temperature with altitude. 13.28 Consider an ideal gas with following distribution of speeds

(i) Calculate Vrms and hence T. 26 ( 3.0 10 kg) m − = *

(ii) If all the molecules with speed 1000 m/s escape from the system, calculate new V_rms and hence T.

Consider a heat engine as shown in Fig. Q₁ and Q₂ are heat added to heat bath T₁ and heat taken from T₂ in one cycle of engine. W is the mechanical work done on the engine. If W > 0, then possibilities are:

(a) Q₁ > Q₂ > 0

(b) Q₂ > Q₁ > 0

(c) Q₂ < Q₁ < 0

(d) Q₁ < 0, Q₂ > 0

Consider a cycle followed by an engine 1 to 2 is isothermal 2 to 3 is adiabatic 3 to 1 is adiabatic Such a process does not exist because

(a) Heat is completely converted to mechanical energy in such a process, which is not possible.

(b) Mechanical energy is completely converted to heat in this process, which is not possible.

(c) Curves representing two adiabatic processes don't intersect.

(d) Curves representing an adiabatic process and an isothermal process don't intersect.

Figure 12.5 shows the P-V diagram of an ideal gas undergoing a change of state from A to B. Four different parts I, II, III and IV as shown in the figure may lead to the same change of state.

(a) Change in internal energy is same in IV and III cases, but not in I and II

(b) Change in internal energy is same in all the four cases

(c) Work done is maximum in case I

(d) Work done is minimum in case II

An ideal gas undergoes isothermal process from some initial state i to final state f. Choose the correct alternatives.

(a) dU = 0

(b) dQ= 0

(c) dQ = dU

(d) dQ = dW

Which of the processes described below are irreversible?

(a) The increase in temperature of an iron rod by hammering it

(b) A gas in a small container at a temperature T₁ is brought in contact with a big reservoir at a higher temperature T₂ which increases the temperature of the gas

(c) A quasi-static isothermal expansion of an ideal gas in cylinder fitted with a frictionless piston

(d) An ideal gas is enclosed in a piston cylinder arrangement with adiabatic walls. A weight W is added to the piston, resulting in compression of gas

Three copper blocks of masses M₁, M₂ and M₃ kg respectively are brought into thermal contact till they reach equilibrium. Before contact, they were at T₁, T₂, T₃ (T₁ > T₂ > T₃ ). Assuming there is no heat loss to the surroundings, the equilibrium temperature T is (s is specific heat of copper)

(a) T= $\frac{{\mathit{T}}_1+{\mathit{T}}_2+{\mathit{T}}_3}{3}$

(b) T= $\frac{{\mathit{M}}_1{\mathit{T}}_1+{\mathit{M}}_2{\mathit{T}}_2+{\mathit{M}}_3{\mathit{T}}_3}{{\mathit{M}}_1+{\mathit{M}}_2+{\mathit{M}}_3}$  

(c)  T= $\frac{{\mathit{M}}_1{\mathit{T}}_1+{\mathit{M}}_2{\mathit{T}}_2+{\mathit{M}}_3{\mathit{T}}_3}{3({\mathit{M}}_1+{\mathit{M}}_2+{\mathit{M}}_3)}$

(d) T= $\frac{{\mathit{M}}_1{\mathit{T}}_1\mathit{s}+{\mathit{M}}_2{\mathit{T}}_2\mathit{s}+{\mathit{M}}_3{\mathit{T}}_3\mathit{s}}{{\mathit{M}}_1+{\mathit{M}}_2+{\mathit{M}}_3}$   

Consider two containers A and B containing identical gases at the same pressure, volume and temperature. The gas in container A is compressed to half of its original volume isothermally while the gas in container B is compressed to half of its original value adiabatically. The ratio of final pressure of gas in B to that of gas in A is

(a) $2^{\mathit{\gamma }-1}$  

(b) ${\left(\frac{1}{2}\right)}^{\mathit{\gamma }-1}$   

(c) $({\frac{1}{1-\mathit{\gamma }})\mathit{}\mathit{}}^2$  

(d) ${\left(\frac{1}{\mathit{\gamma }-1}\right)}^2$