If the surface of a liquid is plane, then the angle of contact of the liquid with the walls of the container is -

1. Acute angle

2. Obtuse angle

3. 90°

4. 0°

If two soap bubbles of different radii are in communication with each other

1. Air flows from larger bubble into the smaller one

2. The size of the bubbles remains the same

3. Air flows from the smaller bubble into the large one and the larger bubble grows at the expense of the smaller one

4. The air flows from the larger

The surface tension of the soap solution is $25\times {10}^{-3} {\mathrm{Nm}}^{-1}$ . The excess pressure inside a soap bubble of diameter 1 cm is 

1. 10 Pa

2. 20 Pa

3. 5 Pa

4. None of the above

When two soap bubbles of radius ${\mathrm{r}}_1$ and ${\mathrm{r}}_2$ (${\mathrm{r}}_2$>${\mathrm{r}}_1$) coalesce, the radius of curvature of the common surface is

1. ${\mathrm{r}}_2-{\mathrm{r}}_1$

2.  $\frac{{\mathrm{r}}_2-{\mathrm{r}}_1}{{\mathrm{r}}_2{\mathrm{r}}_1}$

3. $\frac{{\mathrm{r}}_2{\mathrm{r}}_1}{{\mathrm{r}}_2-{\mathrm{r}}_1}$

4. ${\mathrm{r}}_2+{\mathrm{r}}_1$

A long cylindrical glass vessel has a small hole of radius 'r' at its bottom. The depth to which the vessel can be lowered vertically in the deep water bath (surface tension T) without any water entering inside is

1. $4\mathrm{T}/\mathrm{r\rho g}$

2. $3\mathrm{T}/\mathrm{r\rho g}$

3. $2\mathrm{T}/\mathrm{r\rho g}$

4. $\mathrm{T}/\mathrm{r\rho g}$

The excess of pressure inside a soap bubble than that of the outer pressure is

1. $\frac{2\mathrm{T}}{\mathrm{r}}$

2. $\frac{4\mathrm{T}}{\mathrm{r}}$

3. $\frac{\mathrm{T}}{2\mathrm{r}}$

4. $\frac{\mathrm{T}}{\mathrm{r}}$

The pressure of air in a soap bubble of 0.7cm diameter is 8 mm of water above the pressure outside. The surface tension of the soap solution is

1. 100 dyne/cm

2. 68.66 dyne/cm

3. 137 dyne/cm

4. 150 dyne/cm

The pressure inside two soap bubbles are 1.01 and 1.02 atmospheres. The ratio between their volumes is

1. 102 : 101

2. $(102{)}^3:(101{)}^3$

3. 8 : 1

4. 2 : 1

The radii of two soap bubbles are ${\mathrm{r}}_1$ and ${\mathrm{r}}_2$ . In isothermal conditions, two meet together in a vacuum. Then the radius of the resultant bubble is given by

1. $\mathrm{R}=({\mathrm{r}}_1+{\mathrm{r}}_2)/2$

2. $\mathrm{R}={\mathrm{r}}_1({\mathrm{r}}_1{\mathrm{r}}_2+{\mathrm{r}}_2)$

3. ${\mathrm{R}}^2={\mathrm{r}}_1^2+{\mathrm{r}}_2^2$ 

4. $\mathrm{R}={\mathrm{r}}_1+{\mathrm{r}}_2$

When a large bubble rises from the bottom of a lake to the surface, its radius doubles. If atmospheric pressure is equal to that of a column of water height H, then the depth of the lake is

1. H

2. 2H

3. 7H

4. 8H