Q

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

Q 10.2  Explain why

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

Views

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 $\Theta$

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.

$\\T_{SL}+T_{LA}cos\Theta =T_{SA}\\ cos\Theta =\frac{T_{SA}-T_{SL}}{T_{LA}}$

In case of mercury TSA < TSL and therefore $cos\Theta <0$ and therefore $\Theta >\frac{\pi }{2}$ i.e the angle of contact of mercury with glass is obtuse.

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