Q26 of 39 Page 300

The lower end of a capillary tube of radius 1 mm is dipped vertically into mercury. (a) Find the depression of mercury column in the capillary. (b) If the length dipped inside is half the answer of part (a), find the angle made by the mercury surface at the end of the capillary with the vertical. Surface tension of mercury = 0.465 N m-1 and the contact angle of mercury with glass = 135o.

(a) 4.9 mm

(b) 111o


Given, surface tension of mercury,


Radius of the capillary tube,


As the liquid is mercury, it will concave downwards.


Contact angle,


(a)The rise/depression is given by,



(b)Let the angle made by mercury be .


Given, new height(rise),


We know,


—————(1)


And —————(2)


Dividing (1) by (2)






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