Question

If a capillary tube is immersed at first in cold water and then in hot water, the height of capillary rise will be smaller in the second case. Give reason.

Answer 1

The height upto which a liquid rises in capillary tube, is given by:-

h = 2scosθ/rγg

Now, as the surface tension(s) of hot water is less than that of cold water, when a capillary tube is immersed in hot water, it expands. Therefore, its radius increases. As 'δ' decreases and 'r' increases. therefore the height of capillary size(h) will be smaller in hot water than in cold water.