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What is condensation? Give examples from daily life.

Class 6 ScienceNCERT chapter: A Journey through States of Waterइसे हिंदी में पढ़ें

Exam-ready answer

Condensation is the process in which water vapour changes into liquid water on cooling. Air always contains invisible water vapour. When it touches a cold surface, it loses heat and forms tiny water drops. Examples are drops on the outside of a glass of ice water, dew on grass in the morning, and a bathroom mirror fogging up.

Explanation

Take a dry steel tumbler, put some ice cubes in it and wait a few minutes. Tiny water drops appear on its outer surface. This water does not leak from inside, because the drops form even when the tumbler holds only ice. They come from the water vapour present in the air around the tumbler.

The ice makes the outer surface of the tumbler cold. Water vapour in the air that touches this surface gives up heat and cools. On cooling, the gas changes into liquid water and collects as drops. This change of water vapour into liquid water on cooling is called condensation. It is the reverse of evaporation, in which liquid water changes into water vapour.

Many daily events follow the same steps. On cool nights, grass and leaves become cold and water vapour condenses on them as dew. Our breath contains water vapour, so breathing on a mirror or cold spectacles makes them foggy. After a hot bath, the bathroom mirror clouds over. High in the sky, rising water vapour cools and condenses into tiny droplets that form clouds.

Points to remember

  1. Condensation: the change of water vapour (gas) into liquid water on cooling.
  2. Water vapour is always present in air but cannot be seen.
  3. Condensation is the reverse of evaporation.
  4. Examples: drops on a cold glass, dew on grass, fogged mirrors and spectacles, clouds.
  5. Condensation of water vapour high in the atmosphere forms clouds, which lead to rain.

Exam tip

Write the definition with both key words, 'water vapour' and 'cooling', then give at least three examples. Describing the ice-in-a-tumbler activity in two lines makes the answer complete.

Questions students also ask

How do we know the drops on a cold glass do not come from inside it?
Drops form even when the glass contains only ice and is not full to the brim. If coloured water is used inside, the drops outside are colourless. This shows the water comes from water vapour in the surrounding air, not from the glass leaking.
Why do we see dew in the morning?
During a cool night, grass, leaves and other surfaces lose heat and become colder than the air. Water vapour in the air touching these surfaces cools and condenses into small drops. These drops, seen in the early morning, are called dew.
What is the difference between evaporation and condensation?
Evaporation is the change of liquid water into water vapour; it needs heat and makes things dry. Condensation is the change of water vapour into liquid water; it happens on cooling and makes surfaces wet. They are opposite processes.

Chapter labels help you find the topic in your textbook. Check your own edition: chapter names and order can change. These are Know.it explanations, not official NCERT solutions.