Question

Give scientific reasons (in not more than four lines each) for the following:
(i) Meat takes longer to cook on the mountains
(ii) Water remains cool in earthen pitchers
(iii) Ice and salt mixture is used as a freezing agent by manual ice cream makers. (iv)
It is not advisable to sleep under trees during the night.
(v) Greenhouse operators paint their glass roofs white in summer.

Answer 1

(i) Meat takes longer to cook on the mountains: The atmospheric pressure decreases as the altitude increases. The boiling point of water is 100 c at standard atmospheric pressure. At the mountains this atmospheric pressure is less, thus water boils at temperature lower than 100c.Therefore the meat takes longer time to be cooked. This can be overcome by using pressure cookers.

(ii) Water remains cool in earthen pitchers: The water gets evaporated through the pores of earthen pot and in so doing takes more heat from the water in the form of latent heat and gets cooled in turn. While a metal or glass container has no pores and therefore does not permit the evaporation of water which does not get so cooled.

(iii) Ice and salt mixture is used as a freezing agent by manual ice cream makers. Salt lowers down the temperature of ice by decreasing its freezing point. That is why ice and salt mixture is used as freezing agent in ice cream making.

(iv) It is not advisable to sleep under trees during the night. Because plants at night releases carbon dioxide and takes up oxygen.

(v) Greenhouse operators paint their glass roofs white in summer. In summer there is already much hot and white colour has a property of reflection of light to a maximum. And therefore white colour is painted on the roofs in the summer.