NAEST 2017 Screening Test: Boiling of Water

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A vessel containing water is kept on a burner. The heat supplied by the burner raises the water temperature. The water starts boiling when its temperature reaches the boiling point. What happens if another water vessel is kept inside the first vessel? You observe something surprising.

Question: Select the correct option(s)

  1. The temperature of boiling water is less than 100 degree Celsius
  2. The temperature of boiling water is equal to 100 degree Celsius
  3. The temperature of boiling water is more than 100 degree Celsius
  4. The temperature of water inside the small bowl is 100 degree Celsius
  5. The water in small bowl does not boil because its temperature is less than 100 degree Celsius
  6. The water in small bowl does not boil because it is not getting heat required for vaporization

Answer: Options (B) and (D) are correct.

The water changes phase from liquid to gas through vaporization. It absorbs 'latent heat of vaporization' in this process. The water boils at 100 degree Celsius under atmospheric pressure.

The boiling water is at 100 degree Celsius. The water in a small bowl is also at 100 degree Celsius. The water in a small bowl is not boiling because it is not getting the necessary heat for evaporation. The temperature outside and inside the small boil is the same (100 degree Celsius). In the absence of temperature gradient (difference), heat can not be conducted through the material of the bowl.

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