[lovegood]

hi guys, need some help for this question.

a capillary of unknown internal radius was inserted into a pool of mercury into a pool of mercury. the height of mercury within the capillary was depressed 1.6cm below the free liquid. Calculate the internal diameter of the capillary. For the mercury-air interface on glass, the contact angle is 140 degree. for mercury at 298.15K, density= 13.59g/cm3, surface tension=0.4865Nm-1

im not sure how to go about solving this question. is it the same approach for capillary rise, but in this case it's a depression, which is due to the cohesive force being greater than the adhesive force. for capillary rise, 2 x pi x r x surface tension x cos angle = pi x r2 x h x density x g.

[Hunt]

your on the right track except here a negative sign is added since the height decreases :

- r pgh = 2 gamma (Cos theta)

Just solve for r...