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

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(C) \(\theta \) increases and \(h\) decreases

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Detailed explanation

Angle of contact \(\theta \)

\(\cos \theta = \frac{{{T_{SA}} - {T_{SL}}}}{{{T_{LA}}}}\)

when water is on a waxy or oily surface

\({T_{SA}} < {T_{SL}}\cos \theta \,is\,negative\,i.e.,\)

\({90^ \circ } < \theta < {180^ \circ }\)

\(i.e.,\,angle\,of\,contact\,\theta \,increases\)

\(And\,for\,\theta > {90^ \circ }\,liquid\,level\,in\,capillary\,tube\)

\(fall.\,i.e.,\,h\,decreases\)

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