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Two parallel glass plates are dipped partly in the liquid of density 'd' keeping them vertical. If the distance between the plates is 'x', surface tension for liquids is T and angle of contact is \[\theta \], then rise of liquid between the plates due to capillary will be                            [NCERT 1981]

A)             \[\frac{T\cos \theta }{xd}\]

B)                       \[\frac{2T\cos \theta }{xdg}\]

C)             \[\frac{2T}{xdg\cos \theta }\]

D)                      \[\frac{T\cos \theta }{xdg}\]

Correct Answer: B

Solution :

        Let the width of each plate is b and due to surface tension liquid will rise upto height h then upward force due to surface tension = \[2Tb\cos \theta \]                            ?(i) Weight of the liquid rises in between the plates = \[Vdg=(bxh)dg\]                              ?(ii) Equating (i) and (ii) we get ,\[2T\cos \theta =bxhdg\]             \[\therefore h=\frac{2T\cos \theta }{xdg}\]