Question

Water stays cool in an earthen pot (matki) during summer. Why?
What will happen if this earthen pot is painted from the outside?

Answer 1

When the water oozes out of the pores of an earthen pot, during the hot summers, it begins to evaporate rapidly. Water molecules source latent heat of vapourisation from the water inside to achieve this purpose. This heat energy transfer causes the water contained in the pot to cool down.

If the earthen pot is painted from outside, the pores on the outer surface will get covered. This will disable the seeping water to come into direct contact with the dry air. Vaporization will not take place as water will not be able to escape into the atmosphere. Hence the water will not be able to cool down fast.