The excess pressure inside a spherical soap bubble of radius $1 \,cm$ is balanced by a column of oil (specific gravity $= 0.8$), $2 \,mm$ high. The surface tension of the bubble is: (in $\,N/m$)

$A$ soap bubble $(S.T = 30\, dyne/cm)$ has a radius of $1\, cm$. The work done in doubling its radius would be ........ $ergs$.

The radii of two soap bubbles are $r_1$ and $r_2$. In isothermal conditions,they meet together in a vacuum. Then the radius of the resultant bubble is given by

$A$ soap bubble (surface tension $= T$) is charged to a maximum surface density of charge $= \sigma$. When it is just about to burst,its radius $R$ is given by:

The surface tension and vapour pressure of water at $20^{\circ} C$ are $7.28 \times 10^{-2} \, N/m$ and $2.33 \times 10^{3} \, Pa$ respectively. What is the radius of the smallest spherical water droplet which can form without evaporating at $20^{\circ} C$?

The force required to separate two glass plates of area $10^{-2} \, m^2$ with a film of water $0.05 \, mm$ thick between them is ...... $N$. (Surface tension of water is $70 \times 10^{-3} \, N/m$)