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

$A$ 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 $TL$)

It is better to wash clothes in hot water than in cold water. Explain.

$A$ ring is cut from a platinum tube with an internal diameter of $8.5\, cm$ and an external diameter of $8.7\, cm$. It is supported horizontally from the pan of a balance so that it comes in contact with the water in a glass vessel. If an extra $3.97\, g$ weight is required to pull it away from the water,the surface tension of water is ......... $dyne\, cm^{-1}$.

The force required to take away a flat circular plate of radius $2 \, cm$ from the surface of water will be (the surface tension of water is $70 \, dyne/cm$).

$A$ rectangular film of liquid is extended from $(4 \, cm \times 2 \, cm)$ to $(5 \, cm \times 4 \, cm).$ If the work done is $3 \times 10^{-4} \, J,$ the value of the surface tension of the liquid is ............ $N \, m^{-1}$