Exercise-1.5 Page: ( matter in our surroundings )

1.Why does a desert cooler cool better on a hot dry day?

Solution: It is because the temperature is high and it is less humid on a hot dry day which enables better evaporation. High levels of this evaporation provide better cooling effects.

2. How does the water kept in an earthen pot (matka) become cool during summer?

Solution: An earthen pot is porous in nature. These tiny pores facilitate penetration of water and hence their evaporation from the pot surface. The process of evaporation requires energy which is contributed by water in the pot as a result of which water turns cooler.

3.Why does our palm feel cold when we put on some acetone or petrol or perfume on it?

Solution: Acetone, petrol, and perfume are volatile substances that get evaporated when they come in contact with air. Evaporation is facilitated as it uses energy from palm hence leaving a cooling effect on our palms.

4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?

Solution: A saucer has a larger surface area than a cup which promotes quicker evaporation hence the tea or milk in a saucer cools down faster.

5. What type of clothes should we wear in summer?

Solution: In summer, it is preferred to wear light-coloured cotton clothes because light colour reflects heat and cotton materials have pores that absorb sweat, facilitating their evaporation hence causing a cooling effect in the skin.

Category: Class 9th

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