Wax is coated on the inner wall of a capillary tube and the tube is...

Wax is coated on the inner wall of a capillary tube and the tube is then dipped in water. Then, compared to the unwaxed capillary, the angle of contact

\theta

and the height

h

upto which water rises change. These changes are :

Options

A $\theta$ increases and $h$ also increases
B $\theta$ decreases and $h$ also decreases
C $\theta$ increases and $h$ decreases
D $\theta$ decreases and $h$ increases

Correct answer

C. $\theta$ increases and $h$ decreases

Step-by-step solution

Angle of

\operatorname{contact} \theta

\cos

\theta=\frac{\mathrm{T}_{\mathrm{SA}}-\mathrm{T}_{\mathrm{SL}}}{\mathrm{T}_{\mathrm{LA}}}

when water is on a waxy or oily surface

\mathrm{T}_{\mathrm{SA}} \lt \mathrm{T}_{\mathrm{SL}} \cos \theta

is negative i.e., 90^{{}^{\circ}} <

\theta

< 180^{{}^{\circ}} i.e., angle of contact

\theta

increases And for

\theta \gt 90^{{}^{\circ}}

liquid level in capillary tube fall. i.e., h decreases

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