Question

The pressure cooker is based on the principle that boiling point of water increases with the ________:
A. Increase in pressure
B. Decrease in pressure
C. Both a & b
D. None of these

Answer 1

Hint: Boiling point temperature of the water is a temperature at which the water molecules on the surface of water get converted into water vapors. This happens when the molecules on the surface of water overcome the pressure above the surface of the water so that it can escape in the atmosphere. The boiling point of pure water is 273K.

Complete step by step answer:
For a molecule to get an escape in the atmosphere, it must achieve enough energy so that it can overcome the surface tension of water and then the atmospheric pressure. The temperature corresponding to this energy is called the boiling point. If the pressure above the surface of the water is decreased, its molecules need less energy to escape to the atmosphere, which also means that the boiling point of that liquid is decreased. This is the reason that water boils faster in the hilly area where elevation is more so that atmospheric pressure is less.
Working of a pressure cooker: When food is placed inside the pressure cooker, due to heat provided to it, water starts to convert to steam and hence increasing pressure. Once sufficient pressure is increased, it gets dominated over the boiling point. This means now the boiling point is elevated, so all the heat being provided to the cooker goes to cook the food. This decreases the time of cooking food by approximately 3 times.

Hence A is the correct answer.

Note:
It must be noted that the cookers are designed in such a way that the pressure at some point balances the weight of the whistle, indicating that pressure has got sufficiently high so one should lower the heat. Cookers are used to cook the food faster and in a moist environment. For example, it used to cook red meat which is hard in nature and needs time to get cooked.