Q 10.2 Explain why
(a) The angle of contact of mercury with glass is obtuse, while that of water with glass is acute.
TSL = Surface tension corresponding to the solid-liquid layer
TLA = Surface tension corresponding to liquid-air layer
TSA = Surface tension corresponding to solid-air layer
The angle of contact is
Since the liquid is not flowing over the solid surface the components of TSL, TLA and TSA along the solid surface must cancel out each other.
In case of mercury TSA < TSL and therefore and therefore i.e the angle of contact of mercury with glass is obtuse.