A capillary tube of radius r can support a liquid of weight 6.28 x 10^-4 N. If the surface tension of the liquid is 5 x 10^-2N/m. The radius of capillary must be

• $2.0\times {10}^{-3}\mathrm{m}$

• $2.0\times {10}^{-4}$m

• 1.5$\times {10}^{-3}\mathrm{m}$

• $12.5\times {10}^{-4}\mathrm{m}$

The soap bubbles have radii in the ratio 2: 1 ratio of excess pressure in side there is

• 1:4

• 4:1

• 2:1

• 1:2

The radius R of the soap bubble is doubled under isothermal condition. If T be the surface tension of soap bubble. The work done in doing so is given by

• $32 {\mathrm{\pi R}}^2\mathrm{T}$

• $24 {\mathrm{\pi R}}^2\mathrm{T}$

• $8 {\mathrm{\pi R}}^2\mathrm{T}$

• $4 {\mathrm{\pi R}}^2\mathrm{T}$

An ice-cube of density 900 kg /m³ is floating in water of density 1000 kg / m³. The percentage of volume of ice-cube outside the water is

• 20%

• 35%

• 10%

• 25%

A tank is filled with water upto height H. When a hole is made at a distance h below the level of water. What will be the horizontal range of water jet?

• $2 \sqrt{\mathrm{h} \left(\mathrm{H} - \mathrm{h}\right)}$

• $4 \sqrt{\mathrm{h} \left(\mathrm{H} + \mathrm{h}\right)}$

• $4 \sqrt{\mathrm{h} \left(\mathrm{H} - \mathrm{h} \right)}$

• $2 \sqrt{\mathrm{h} \left(\mathrm{H} + \mathrm{h}\right)}$

A charged oil drop is suspended in uniform field of 3 x 10⁴ V/m so that it neither falls nor rises. The charge on the drop will be (Take the mass of the charge = 9.9 x 10^-15 kg and g = 10 m/s² )

• 3.3 × 10^-18 C

• 3.2 × 10^-18 C

• 1.6 × 10^-18 C

• 4.8 × 10^-18 C

A frame made of metallic wire enclosing a surface area A is covered with a soap film. If the area of the frame of metallic wire is reduced by 50%, the energy of the soap film will be changed by

• 100%

• 75%

• 50%

• 25%

The potential energy of a molecule on the surface of a liquid compared to one inside the liquid is

• zero

• lesser

• equal

• greater

99.

Aerofils are so designed that the speed of air

• on top side is more than on lower side

• on top side is less than on lower side

• is same on both sides

• is turbulent

Two glass plates are separated by water. If surface ension of water is 75 dyne/cm and area of each plate wetted by water is 8 cm² and the distance between the plates is 0.12 mm, then the force applied to separate the two plates is

• 10² dyne

• 10⁴ dyne

• 10⁵ dyne

• 10⁶ dyne