11.

At which of the following temperatures, the value of surface tension of water is minimum

• 4º C

• 25º C

• 50º C

• 75º C

Work done in splitting a drop of water of 1 mm radius into 64 droplets is (surface tension of water = 72x 10^-3 J/m²)

• 2.0 x 10^-6 J

• 2.7 x 10^-6 J

• 4 x 10^-6 J

• 5.4 x 10^-6 J

A black body at 227°C radiates heat at the rate of 7 cal/cm² -s. At a temperature of 727°C. the rate of heat radiated in the same units will be

• 80

• 60

• 50

• 112

The vertical extension in a light spring by a weight of 1 kg suspended from the wire is 9.8 cm. The period of oscillation is

• 20π s

• 2π s

• $\frac{2\mathrm{\pi }}{10}\mathrm{s}$

• 200$\mathrm{\pi }$ s

A particle of mass 10 g is describing SHM along a straight line with a period of 2 s and amplitude of 10 cm. Its kinetic energy when it is at 5 cm from its equilibrium position is

• 3.75 π² erg

• 375 π² erg

• 0.375 π² erg

• 37.5 π² erg

The angular amplitude of a simple pendulum is θ₀ The maximum tension in its string will be

• mg(1 - θ₀)

• mg(1 + θ₀)

• mg(1 - ${\mathrm{\theta }}_0^2$)

• mg(1 + ${\mathrm{\theta }}_0^2$)

It is possible to recognize a person by hearing his voice even if he is hidden behind a solid wall. This is due to the fact that his voice

• has a definite capacity

• has a definite quality

• has definite pitch

• can penetrate the wall

The velocity of sound in air at NTP is 330 m/s. What will be its value when the temperature is doubled and pressure is halved?

• 330 m/s

• 165 m/s

• 330$\sqrt{2}$ m/s

• $\frac{330}{\sqrt{2}}\mathrm{m}/\mathrm{s}$

Two gases A and B at same pressure contain a number of moles n₁ and n₂. Their volume temperature graphs are shown in the figure. Then the ratio n₁/n₂

• 1

• 1/2

• 1/3

• 3

A source of sound emits 200 $\mathrm{\pi }$W power which is uniformly distributed over a sphere of 10 m radius. What is the loudness of sound on the surface of a sphere?

• 200 dB

• 200π dB

• 120 dB

• 120π dB