$A$ paper disc of radius $R$ from which a circular hole of radius $r$ is cut out,is floating in a liquid of surface tension $T$. The force on the disc due to surface tension will be

When water is heated,bubbles form at the bottom and detach to rise. Let the radius of the bubble be $R$. The bubble is in circular contact with the bottom of the container with a radius $r$. If $r \ll R$ and the surface tension of water is $T$,find the value of $r$ just before the bubble detaches from the container. (Density of water is $\rho_w$)

$A$ rectangular film of liquid is expanded from $(5 \text{ cm} \times 4 \text{ cm})$ to $(7 \text{ cm} \times 8 \text{ cm})$. If the work done is $3 \times 10^{-4} \text{ J}$,the surface tension of the liquid is (nearly):

The free surface of a liquid has a tendency to contract. This property is called ...... .

With an increase in temperature,surface tension of liquid (except molten copper and cadmium)

Give a reason why some insects are able to walk on the water surface.