21.

Pressure versus temperature graph of an ideal gas is as shown in figure. Density of the gas at point  A is  ρ₀  Density at point B will be

           

• $\frac{3}{4}$ ρ₀

• $\frac{3}{2}$ ρ₀

• $\frac{4}{3}$ ρ₀

• 2ρ₀

The latent heat of vaporisation of a substance is always

• greater than its latent heat of fusion

• greater than its latent heat of sublimation

• equal to its latent heat of sublimation

• less than its latent heat of fusion

A reversible engine converts one-sixth of the heat input into work. When the temperature of the sink is reduced by   62°C, the efficiency of the engine is doubled. The temperatures of the source and sink are

• 99^oC, 37^oC

• 80^oC, 37^oC

• 95^oC, 37^oC

• 90^oC, 37^oC

Graph of specific heat at constant volume for a monoatomic gas is

A liquid is kept in a cylindrical vessel which is being rotated about a vertical axis through the centre of the circular base. If the radius of the vessel is r and angular velocity of rotation is w, then the difference in the heights of the liquid at the centre of the vessel and the edge is

• $\frac{\mathrm{r} \mathrm{\omega }}{2 \mathrm{g}}$

• $\frac{{\mathrm{r}}^2 {\mathrm{\omega }}^2}{2 \mathrm{g}}$

• $\sqrt{2 \mathrm{gr} \mathrm{\omega }}$

• $\frac{{\mathrm{\omega }}^2}{2 {\mathrm{gr}}^2}$

A capillary tube of radius r is immersed in water and water rises in it to a height h. The mass of water in the capillary tube is 5 g. Another capillary tube of radius 2 r is immersed in water. The mass of water that will rise in this tube is

• 2.5 g

• 5.0 g

• 10 g

• 20 g

Five sinusoidal waves have the same frequency 500 Hz but their amplitudes are in the ratio 2 : $\frac{1}{2} : \frac{1}{2} : 1 : 1$ and their phase angles 0, $\frac{\mathrm{\pi }}{6}, \frac{\mathrm{\pi }}{3}, \frac{\mathrm{\pi }}{2} \mathrm{and} \mathrm{\pi }$ respectively. The phase angle of resultant wave obtained by the superposition of these five waves is

• 30^o

• 45^o

• 60^o

• 90^o

The second overtone of an open pipe has the same frequency as the first overtone of a closed pipe 2 m long. The length of the open pipe is

• 8 m

• 4 m

• 2 m

• 1 m

Let T₁ and T₂ be the time periods of springs A and B when mass M is suspended from one ·end of each spring. If both springs are taken in series and the same mass M is suspended from the series combination, the time period is T then

• T₁ + T₂ +T₃

• $\frac{1}{\mathrm{T}} = \frac{1}{{\mathrm{T}}_1} + \frac{1}{{\mathrm{T}}_2}$

• T² = ${\mathrm{T}}_1^{ 2} + {\mathrm{T}}_2^{ 2}$

• $\frac{1}{{\mathrm{T}}^2} = \frac{1}{{\mathrm{T}}_1^{ 2}} + \frac{1}{{\mathrm{T}}^2}$

Assertion:  Water kept in an open vessel will quickly evaporate on the surface of the moon. 

Reason:  The temperature at the surface of the moon is much higher than boiling point of water.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.