question_answer

If a capillary tube is immersed at first in cold water and then in hot water, the height of capillary is smaller in the second case. Why?

Answer:

                The height up to which a liquid rises in a capillary tube is given by \[h=\frac{2\sigma \cos \theta }{r\rho g}\] The surface tension (\[\sigma \]) of hot water is less than that of cold water. Moreover, capillary tube expands in hot water, so its radius r increases. So capillary rise h is smaller in hot water than in cold water.