Question

It takes much longer to cook food in the hills than in the plains, because
A. In the hills the atmospheric pressure is lower than in the plains and therefore water boils at a temperature lower than the ${{100}^{o}}C$ causing an increase in cooking time.
B. Due to low atmospheric pressure on the hills, the water boils at a temperature higher than ${{100}^{o}}C$and therefore water takes longer to boil
C. In the hills the atmospheric density is low and therefore a lot of heat is lost to the atmosphere
D. In the hills the humidity is high and therefore a lot of heat is absorbed by the atmosphere leaving very little heat for cooking.

Answer 1

Hint:Define the variation of pressure with change in altitude. Explain why temperature drops with the height and why the boiling point of liquid decreases with increase in altitude. Use this concept to give the answer to the question.


Complete step by step solution:
The air pressure is comparatively less in high altitudes than at a low altitude. At the sea level, the air pressure is the highest. As the altitude increases, the number of air molecules in the air decreases, and with the decrease of air molecules, the pressure also decreases.
The pressure of air is due to the movement and collision of the gas particles in the air. With an increase in altitude, the number of gas-particles decreases, and thus the collision between the gas-particles also decreases. So, the pressure also decreases.
Now, with an increase in pressure the boiling temperature of the water also decreases. The water boils at the point where the vapour pressure of the water exceeds the air pressure. Near the earth’s surface the boiling temperature of the water is ${{100}^{o}}C$. But as the altitude increases, the air pressure decreases and hence the temperature needed to exceed vapour pressure then the air pressure also decreases. So, at high altitude the boiling temperature of water decreases.
So, we can say that it takes much longer to cook food in the hills than in the plains because In the hills the atmospheric pressure is lower than in the plains and therefore water boils at a temperature lower than the ${{100}^{o}}C$ causing an increase in cooking time.

The correct option is (A).

Note:The low pressure at high altitude can be defined due to two reasons. First the density of air molecules decreases and the second, the gravity pulls the air with less force at high altitude.
Altitude sickness is due to this low pressure at high altitudes. Due to low pressure, we have less oxygen to breathe and this leads to altitude sickness.