03 Feb How does water become cooler in an earthen pitcher?
We are back with another exciting story for your physics tuition. Your physics tuition will always come up with interesting facts about physics. You may know that in summer, water when kept in earthen pitchers or pots turn cooler after some hours. But, this drop in water temperature is not experienced if it is kept in containers made of glass or metal. Do you know why it is so? Let your physics tuition give you the answer.
This procedure of water being cooled can be very well explained with the help of a principle of physics that is quite well known. This principle states that cooling is caused by evaporation. During evaporation of liquid, its temperature decreases due to the heat needed for the vaporisation process are provided itself by the liquid. Because of the heat loss, the liquid temperature falls. The earthen pitcher contains numerous pores throughout its surface. At the time when water is kept in the earthen vessel, it oozed out from these numerous pores and gets evaporated. The heat required for this evaporation is taken from the water present inside the pitcher, thereby cooling it. But, in the case of water kept in containers made of glass or metal (which do not have such pores within their surfaces), no water oozes out of the vessels. So, there is no question of water being evaporated from the surfaces. Since there is no evaporation, there is also no question of water placed inside getting cooler.
This same principle applies, when we feel cooler in summer under a fan as sweats come out from numerous pores present in our body and get evaporated. This principle is also used by dogs by hanging their tongues out, thereby exposing it to the outer air (dogs have sweat buds on their tongues and not throughout their body like us) and utilizing the evaporation effect. Watering the streets in summer can also give the same result.
We hope you enjoyed this lesson from physics tuition. We will be back with more such interesting findings in our next physics tuition.
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