A thin film of water is formed between two straight parallel wires each of length 8 cm separated by distance of 0.6 cm . The work done to increase the distance between the wires to 0.8 cm is (Surface tension of water $=0.07 \mathrm{Nm}^{-1}$ )

A rain drop of diameter 1 mm falls with a terminal velocity of $0.7 \mathrm{~ms}^{-1}$ in air. If the coefficient of viscosity of air is $2 \times 10^{-5} \mathrm{~Pa}$-s, the viscous force on the rain drop is

An air bubble rises from the bottom to the top of a water tank in which the temperature of the water is uniform. The surface area of the bubble at the top of the tank is $125 \%$ more than its surface area at the bottom of the tank. If the atmospheric pressure is equal to the pressure of 10 m water column, then the depth of water in the tank is

If $W_1$ is the work done in increasing the radius of a soap bubble from ' $r$ ' to ' $2 r$ ' and $W_2$ is the work done in increasing the radius of the soap bubble from ' $2 r$ ' to ' $3 r$ ', then $W_1: W_2=$