Question

When a capillary is dipped vertically in water, rise of water in capillary is 'h'. The angle of contact is zero. Now the tube is depressed so that its length above the water surface is `"h"/2.` The new apparent angle of contact is ______.

cos 0° = 1

Options

• sin^-1 (0.5)

• cos^-1 (0.5)

• cos^-1 (0.7)

• sin^-1 (0.7)

Answer 1

When a capillary is dipped vertically in water, rise of water in capillary is 'h'. The angle of contact is zero. Now the tube is depressed so that its length above the water surface is `"h"/2.` The new apparent angle of contact is cos^-1 (0.5).

Explanation:

`T = ("rh"rhog)/(2costheta)=("rh"^'rhog)/(2costheta^')`

`thereforecostheta^'/costheta="h"^'/"h"=1/2=0.5`

∴ cos θ' = 0.5cos 0 = 0.5

∴ θ' = cos^-1 (0.5)