question_answer

What will be the angle of contact of a liquid relative to a solid, if forces of adhesion and cohesion are equal?

A) \[0{}^\circ \]                                      

B) \[30{}^\circ \]

C) \[90{}^\circ \]

D) none of these

Correct Answer: D

Solution :

Angle of contact is the angle between the tangent to the periphery of the point of contact with the solid, and the surface of the solid. \[\angle COB={{90}^{o}}+{{45}^{o}}={{135}^{o}}\] Given,        \[{{F}_{A}}={{F}_{C}}\] Hence, OA makes an angle of\[67.5{}^\circ \]with OC and OB. \[\therefore \]Angle of contact\[={{67.5}^{o}}-{{45}^{o}}={{22.5}^{o}}\]