Water (surface tension 70 dyn/cm, contact angle 0 deg) rises 6 cm in a glass capillary. In the same capillary, a different liquid of surface tension 140 dyn/cm, contact angle 60 deg, and relative density 2 will rise to a height of

12 cm
24 cm
3 cm
6 cm

Correct answer: 3 cm

Solution

Since the same capillary is used, r and g are common. The rise is proportional to T*cos(theta)/rho. Computing the ratio with the given values shows the new liquid rises to half the water height, i.e., 3 cm.

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