Question

A long glass capillary tube is dipped in water. It is known that water wets glass. The water level rises by h in the tube. The tube is now pushed down so that only a length h/2 is outside the water surface. The angle of contact of the water surface at the upper end of the tube will be

(a) 30° 

(b) 45° 

(c) tan^-1 2 

(d) 60°

Answer 1

Correct Answer is: (d) 60°

In (1) 2πrs = πr²hρg.

In (2) 2πrscos θ = πr2 (h/2) ρg.

Dividing, cos θ = 1/2

or θ = 60°.