Q27 of 65 Page 20

On a hot sunny day, why do we feel pleasant sitting under a tree?

On a hot sunny day, we feel pleasant sitting under a tree because:

i. As we know that tree has lot of leaves. Leaves continuously loss water through their small pores present in them.


ii. When this lost water from tiny pores comes in contact with the surface of leaf, the water evaporates.


iii. This evaporation causes cooling effect.


iv. This makes the surrounding cool.


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25

How are particles of matter affected with increasing or reducing

pressure at a given temperature?

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Why is it advisable to use pressure cooker at higher altitudes for cooking food?

 28

(i) Give reason.

(a) Plasma is found in the stars.


(b) The molecules of a solid have the strongest intermolecular forces.


(ii) Out of four gases Cl2, CO2, CH4, N2, which gas would diffuse most rapidly and why?

 29

When ice at –10°C is slowly heated, temperature of ice gradually increases till 0°C, the temperature of the system remains constant when the ice change into water and then further rises. Explain the observation.