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NCERT Solutions Curiosity Chapter 8 .6 Cooling Effect — In-text Questions

Book page 1568 Updated on2026-09-05

Q1.
Aavi asks, “Why is the water in the earthen pot so cold? I never observed water getting cold in a stainless steel pot.” What do you think is the reason?
Answer

The reason is evaporation, and the cooling effect it produces.

  1. An earthen matka is made of baked clay, which is full of very fine pores.
  2. Water slowly seeps through these pores and appears as a thin film of moisture on the outer surface — that is why a matka always feels a little damp.
  3. This film of water evaporates into the air.
  4. To evaporate, water needs heat, and it takes that heat from the pot and from the water still inside it.
  5. Losing heat, the water inside becomes cooler — and the process goes on all day.

Why a stainless steel pot does not do this: steel has no pores. No water can reach the outer surface, so there is nothing to evaporate and no heat is taken away. The water inside simply stays at room temperature.

Water seeps out through the pores → evaporates → takes heat from the pot and the water inside → the water becomes cold
Why the matka works best in dry summer heat: evaporation is fastest when the air is hot and dry and moving. That is exactly the weather in a Rajasthan or Vidarbha summer, which is why a matka can keep water several degrees cooler than the room. During the humid monsoon the same matka cools far less, because evaporation slows down.
Tip: Keep the matka in a shaded, airy place and cover it with a wet cloth. Both increase evaporation from the outside and make the water inside even colder. Never wrap it in plastic — that stops evaporation and defeats the whole purpose.
Q2.
What are the other examples of cooling effect?
Answer

Anywhere water evaporates, cooling follows. The chapter itself names sprinkling water on the floor or the roof in summer. Here is a fuller list:

ExampleWhat evaporates, and what gets cooled
SweatingSweat evaporates from the skin and takes heat from our body — this is how the body controls its temperature
Sitting under a fanMoving air makes the sweat evaporate faster, so we feel cooler even though the fan adds no coldness
Matka and surahiWater seeping through the clay evaporates and cools the water inside
Sprinkling water on the floor or the terraceThe water evaporates and cools the floor and the air just above it
Hanging wet khus or jute curtains at the doorAir passing through is cooled as the water in the curtain evaporates
Desert coolerAir is drawn through wet pads; the water evaporates and the air comes out cool
Sanitiser or spirit on the skinThe alcohol evaporates very fast and the palm feels cold
A wet cloth on the forehead in feverWater evaporating from the cloth carries heat away from the head
A dog panting; a buffalo lying in a pondWater evaporating from the tongue or the wet skin cools the animal
The single rule behind all of them: evaporation is a cooling process. A liquid cannot turn into vapour without taking in heat, and it takes that heat from whatever it is touching — skin, clay, floor or air.
Q3.
How do you feel when you rub sanitiser on your hands?
Answer

The palm feels distinctly cold, and the coldness is strongest just as the sanitiser is disappearing. Blowing on the hand makes it feel colder still.

Why:

  • Sanitiser is mostly alcohol, which evaporates very quickly at room temperature.
  • Rubbing spreads it into a thin film, so the exposed area is large and evaporation is very fast.
  • The evaporating liquid takes the heat it needs from your skin, so the skin loses heat and feels cold.
  • Blowing adds air movement, which speeds the evaporation up further — hence the extra chill.
The connection Aavi makes: Now, I can understand why we feel cooler if we sit under a fan! The wind helps the sweat to evaporate and cools us. Sanitiser on the palm and sweat on the body work in exactly the same way — the fan does not blow cold air, it only helps the liquid evaporate.
Try This — this is also the first Learning further task: wet one hand and leave the other dry, then blow across both. Only the wet hand feels cold, which proves that the cooling comes from the evaporating water and not from the air being cold.
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