Hairs of a shaving brush cling together when it is removed from water due to

$A$ thin metal disc of radius $r$ floats on the water surface and bends the surface downwards along the perimeter,making an angle $\theta$ with the vertical edge of the disc. If the disc displaces a weight of water $W$ and the surface tension of water is $T$,then the weight of the metal disc is:

$A$ drop of some liquid of volume $0.04 \ cm^{3}$ is placed on the surface of a glass slide. Then another glass slide is placed on it in such a way that the liquid forms a thin layer of area $20 \ cm^{2}$ between the surfaces of the two slides. To separate the slides a force of $16 \times 10^{5} \ dyne$ has to be applied normal to the surfaces. The surface tension of the liquid is (in $dyne \ cm^{-1}$):

$A$ wooden stick $2 \, m$ long is floating on the surface of water. The surface tension of water is $0.07 \, N/m$. By putting soap solution on one side of the stick,the surface tension is reduced to $0.06 \, N/m$. The net force on the stick will be ....... $N$.

Why do colours and lubricating oil have less surface tension?

$A$ square frame of each side $L$ is dipped in a soap solution and taken out. The force acting on the film formed is ($T =$ surface tension of soap solution). (in $TL$)