Question

12. (a) Define evaporation. How does it causes cooling effect?
(b) How does surface area, temperature and humidity effects the rate of evaporation?
13. Give reason -
(a) Water droplet appear on the outer surface of a tumbler containing ice cold water.
(b) People prefer to wear cotton clothes in summer.
(c) On a hot summer day people sprinkle water on the roof or open ground.
14. (a) A liquid generally flow easily. Why?
(b) Why do we feel comfortable under a fan when we are perspiring?
(c) Ice at 0°C appears colder to the mouth than water at 0° C. Why?
15. Give reasons -
(a) Steam produces more severe burns than boiling water.
(b) We are able to sip hot tea faster from a saucer rather than a cup.
(c) Oxygen is gas at room temperature.
(d) What is state of water at following temperatures? (a) 0% (b) 35°C
(e) Convert the following temperatures: (i) 30°C (ii) 443 K.
(c) 100​

Answer 1

Answer:

1) The process of a liquid changing into vapour even below it boiling point its called evaporation.

Explanation:

The cooling caused by evaporation is based on the fact that when liquid evaporates , it draws the latent heat of vaporization from "anything " which it touches . By losing heat , this "anything " gets cooled .

2) a)The rate of evaporation increases on increasing the temperature of the liquid . In other words , the rate of evaporation of a liquid increases on heating. when the temperature of a liquid is increased by heating it, more particles of the liquid get enough kinetic energy to go into vapour state . This increases the rate of evaporation .