Two glass plates of area $10^{-2} \,m^2$ have a $10 \,cm$ thick water film between them. The surface tension of water is $70 \times 10^{-3} \,N/m$. The force required to separate the two glass plates from each other is (in $\,N$)

$A$ wire of length $20 \ cm$ is placed horizontally on the surface of water and is gently pulled up with a force of $1.456 \times 10^{-2} \ N$ to keep the wire in equilibrium. The surface tension of water is (in $N \ m^{-1}$)

An iron needle slowly placed on the surface of water floats because

$A$ needle is $7 \ cm$ long. Assuming that the needle is not wetted by water,what is the weight of the needle,so that it floats on water (in $g \ wt$)? $\left[T = \text{surface tension of water} = 70 \ dyne/cm\right]$ [acceleration due to gravity $= 980 \ cm \ s^{-2}$]

$A$ liquid is coming out from a vertical tube. The relation between the weight of the drop $W$,surface tension of the liquid $T$,and radius of the tube $r$ is given by,if the angle of contact is zero.

Define surface tension and provide its formula in the context of $(i)$ intermolecular forces,$(ii)$ potential energy,and $(iii)$ work done.