Explain why
(a) The angle of contact of mercury with glass is obtuse, while that of water with glass is acute.
The angle between the tangent to the liquid surface at the point of contact and the surface inside the liquid is called the angle of contact (θ).
At the line of contact, the surface forces between the three media must be in equilibrium.
i.e., cos θ = (Ssa - Sla) / Sla
where,
sla is the liquid-air interface,
Ssa is the solid-air interface
The angle of contact θ , is obtuse if Ssa < Sla (as in the case of mercury on glass). This angle is acute if Ssl < Sla (as in the case of water on glass).
181 Views
