Two soap bubbles, one of radius $50 \mathrm{mm}$ and the other of radius $80 \mathrm{mm}$, are brought in contact so that they have a common interface. The radius of the curvature of the common interface is

Two glass Plates are separated by water. If surface tension of water is $75 \mathrm{dyne} \mathrm{per} \mathrm{cm}$ And the area of each plate wetted by water is $8{\mathrm{cm}}^2$ And the distance between the plates is $0.12\mathrm{mm}$, then the force applied to separate the two plates is

A soap film of surface tension $3\times {10}^{-2} \mathrm{T}$ formed in a rectangular frame can support a straw as shown in the figure. If $g=10{ \mathrm{m} \mathrm{s}}^{-2}$, the mass of the straw is

A film of soap solution is trapped between a vertical frame and a light wire $ab$ of length $0.1 m$. If $g=10{ ms}^{-2}$, then the load $W$ that should be suspended from the wire to keep it in equilibrium is$$