Question

The angle of contact for a solid and liquid is less than the 900
. Will the liquid
wet the solid? If a capillary is made of that solid, will the liquid rise or fall in
it?

Answer 1

Given:

The angle of contact for a solid and liquid is less than the 90°.

To find:

• Will the liquid wet the solid?
• If a capillary is made of that solid, will the liquid rise or fall in it?

Solution:

• If the angle of contact between liquid and solid surface is acute (i.e. < 90°), then the surface is said to get wet by the liquid.

• If the angle of contact is obtuse (i.e. >90°), then surface doesn't get wet.

• For example: Angle of contact between glass and water is < 90° (i.e. acute), hence glass is wetted by water.

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• If the solid is used to make a capillary and liquid is placed in it , then liquid will rise in it.

Mathematical proof:

$\therefore \: h = \dfrac{2T \cos( \theta) }{ \rho gh}$

• $\theta$<90°, $\cos(\theta)$ will be positive.

• Hence , liquid will rise.