The maximum force in addition to the weight required to pull a wire frame $5.0\mathrm{cm}$ long from a water surface at a temperature of $20°\mathrm{C}$ is $720 \mathrm{dyne}$. The surface tension of water is

A disc of paper of radius $R$ is floating on the surface of water of surface tension T. If $r=20 \mathrm{cm}$ and $\mathrm{T}=0.070\mathrm{N} {\mathrm{m}}^{-1},$ then the force of surface tension on the disc is

Water rises in a capillary tube to a certain height such that the upward force due to surface tension is balanced by a force of $75\times {10}^{-4}\mathrm{N}$ due to the weight of the liquid. If the surface tension of water is $6\times {10}^{-2}{\mathrm{Nm}}^{-1},$ then the inner circumference of the capillary must be

A wire ring of diameter $14\mathrm{cm}$ is gently lowered to a liquid surface and then pulled up. When the film just breaks, the force required is $0.0616\mathrm{N}$. The surface tension of the liquid is

A ring of radius $0.75\mathrm{cm}$ is floating on the surface of water. If surface tension of water is $0.07\mathrm{N} {\mathrm{m}}^{-1},$ then the force required to lift the ring from the surface of water will be

A glass tube of internal diameter $3.5\mathrm{cm}$ and thickness $0.5\mathrm{cm}$ is held vertically with its lower end immersed in water. The downward pull on the tube due to surface tension (S.T. of water is $0.074\mathrm{N} {\mathrm{m}}^{-1}$) 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 clean glass plate of length $9.8\mathrm{cm},$ breadth $4\mathrm{cm}$ and thickness $0.2\mathrm{cm}$ is suspended vertically with its long side horizontal and with half the side immersed. Pull due to surface tension will be $(\mathrm{S}.\mathrm{T}=0.07\mathrm{N} {\mathrm{m}}^{-1} )$

Two drops of equal radius $r$ coalesce to form a single drop under isothermal conditions. The radius of such a drop would be