Chapter 01 Matter in Our Surroundings Questions-04
Questions
1. Why does a desert cooler cool better on a hot dry day?
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Answer
A desert cooler functions on the basis of evaporation. The rate of evaporation increases with increase in temperature and decrease in humidity. As evaporation increases when the day is hot and dry. So, the desert cooler functions to a better extent.
2. How does the water kept in an earthen pot (matka) become cool during summer?
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Answer
Large number of tiny pores is present on the surface of the earthen pot (matka). The water stored in the earthen pot (matka) evaporates faster through these pores due to the increased exposed surface area. As the’ process of evaporation causes cooling, the stored water inside the earthen pot (matka) becomes cool.
3. Why does our palm feel cold when we put some acetone or petrol or perfume on it?
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Answer
Acetone, petrol, perfume etc., being volatile, evaporate very fast when exposed to larger surfaces. During the process they absorb the required latent heat of vaporization from the palm (if kept on palm). So, the process causes Cooling and the palm feels cool.
4. Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
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Answer
A liquid has large surface area in a saucer than in a cup. Thus, it evaporates faster and cools faster in a saucer than in a cup. For this reason we able to sip hot tea or milk faster from a saucer rather than a cup.
5. What type of clothes should we wear in summer?
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Answer
We should wear light colored cotton clothes in summer because
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Cotton is a good absorber of water/sweat. It provides more surface area for the sweat to evaporate.
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Light colours absorb less heat.
So, wearing light coloured cotton clothes helps us feeling cool and comfortable.
