Home » UPSC CDS-1 » After a hot sunny day, people sprinkle water on the roof-top because :

After a hot sunny day, people sprinkle water on the roof-top because :

June 1, 2025 by rawan239

After a hot sunny day, people sprinkle water on the roof-top because :

water helps air around the roof-top to absorb the heat instantly

water has lower specific heat capacity

water is easily available

water has large latent heat of vaporisation

This question was previously asked in

UPSC CDS-1 – 2016

Download PDF Attempt Online

The correct option is D) water has large latent heat of vaporisation.

When water is sprinkled on a hot surface like a rooftop, it evaporates. Evaporation is a process that requires energy (heat). This energy is absorbed from the surroundings, including the rooftop itself and the air, as the water changes from liquid to gas phase. The latent heat of vaporisation is the amount of heat energy required to change a substance from a liquid to a gas at a constant temperature. Water has a relatively high latent heat of vaporisation, meaning it absorbs a significant amount of heat from the rooftop during evaporation, leading to a substantial cooling effect.

Other options are less accurate or irrelevant. While water absorbs heat, the primary cooling mechanism here is the energy required for the phase change (latent heat), not simple heat absorption in liquid form (specific heat capacity). A higher specific heat capacity means it takes more energy to raise the temperature of water, which is also a factor in moderating temperature, but the cooling on a hot day is mainly due to the heat removed during evaporation. Water availability is a practical reason for using it, not the scientific principle behind the cooling.

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