Question

Give reasons:
A). After a hot sunny day, we sprinkle water on the roof or open ground.
B). Perspiration keeps our body cold.
C). Ice is rubbed on the burnt part of the skin.

Answer 1

Hint: Evaporation is a surface phenomenon in which particles of the surface of the liquid evaporate by gaining energy from surroundings and therefore lowering the temperature of its surroundings.

Complete step-by-step solution:
(a). On a hot summer day, when we sprinkle water on the roof or open ground, it evaporates quickly because of the heat of the sun. Evaporation is a kind of vaporization that occurs on the surface of the liquid as it changes into the gas phase. When a molecule gains energy from the surrounding and escapes as the gas molecule, it lowers the internal energy of the surrounding. Therefore, decreases the temperature of the surroundings.
(b). Perspiration, another name for sweating, is a process of releasing sweat from the sweat glands in our body. When the temperature of our surroundings is higher than our normal body temperature, sweat glands release sweat. When sweat evaporates after absorbing the energy from the surrounding, it gives us a cooling effect. Thus, sweating helps us in maintaining our body temperature.
(c). When ice is rubbed on the burnt part of the skin, it absorbs heat from the burnt part and therefore lowers the temperature of the burnt part. This cooling effect helps us in relieving the burning sensation.

Note: Ice has more cooling effect than water. This is because of the heat that is required to convert ice into water, known as latent heat.
Evaporation mostly occurs below the boiling point of the liquid. During this process, only surface liquid gets evaporated.