Question

The contact angle determines whether liquid will rise or get depressed along a solid surface. Select the correct statement regarding the same.

(a) If contact angle is found to be less than 90°, the liquid will have raise along the solid surface

(b) If contact angle is found to be greater than 90°, then liquid will have depressed along the solid surface

(c) Liquid always rises along solid surface, irrespective of contact angle

(d) Liquid always gets depressed along solid surface, irrespective of contact angle

This question was posed to me in an interview for job.

My question comes from Fluids Mechanical Properties topic in chapter Mechanical Properties of Fluids of Physics – Class 11

Answer 1

Correct option is (a) If contact angle is found to be less than 90°, the liquid will have raise along the solid surface

The explanation: A liquid rises or gets depressed along a solid surface such that its surface at that place is perpendicular to the net force. Near the solid and water interface the particles of fluid are acted upon by forces from solid & liquid particles and also gravity. If the resultant force vector on those fluid particles passes through the solid surface, the surface of fluid has to rise to ensure that net force is perpendicular to its surface. When liquid rises the contact, angle becomes less than 90°. Refer to the diagram given.