Explain why (a) The angle of contact of mercury with glass is obtuse , while of water with glass is acute .

Explain why (a) The angle of contact of mercury with glass is obtuse

1.	Explain why (a) The angle of contact of mercury with glass is obtuse , while of water with glass is acute .
Answer» Solution :Let a drop of a LIQUID (L) is on a solid surface S PLACED in AIR A. The air is the medium around drop . The surface tensions are SHOWN on drop . `S_(SL)=` The surface tension corresponding to solid -liquid layer . `S_(LA)` = The surface tension corresponding to liquid - air layer. `S_(SA)` = The surface tension corresponding to solid - air layer. `theta` = angle of contact `S_(LA)costheta+S_(SA)=S_(SL)` For the mercury glass interface , `S_(SA)ltS_(SL)`Therefore , `costheta` is negative . Thus `theta` is an acute angle.