Question

Give reason for the following:

a) Steam causes more severe burns than boiling water.


b) It is easy to prepare food in pressure cookers.


c) Wet clothes get dry at room temperature.


d) Water droplets get spherical shape.


e) Closed glass bottles filled with water should not be kept in freezer.


f) Soap helps in removing dirt from clothes.

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Answer 1

1. Steam causes more severe burns than boiling water because steam contains more heat in the form of latent heat, as compared to boiling water at the same temperature.
2. Cooking is fast in pressure cooker just because the trapped steam increases the atmospheric pressure inside the cooker. At that pressure, boiling point of water is increased and this higher temperature cooks food faster.
3. The concentration of water molecules in the air is commonly called the "humidity". The more humid the surrounding air, the slower a wet object dries. Returning to our wet clothes hung up to dry, they will dry more quickly in a room with dry air than in a room with humid air
4. Raindrops take up the spherical shape due to the surface tension of water which is caused due to the tendency of water molecules to stick together. The spherical shape is having the least possible surface area due to which it can resist any of the external force in the atmosphere.
5. A freezer lowers down the temperature due to which substance can get cold. So, whenever a glass bottle completely filled with water is kept in a freezer the water inside the bottle becomes cool and after attaining a certain temperature it starts expanding. When it is expanded sufficiently the water bottle may burst
6. By decreasing surface tension, this dual quality helps to reduce soil. As the soap is rubbed on a dirty fabric, the soap's hydrophobic molecule holds the dirt molecule on the cloth and the water holds the hydrophilic molecule. The hydrophobic molecule draws out the dirt while rubbing and forms a micelle