Question

Pressure cooker reduces cooking time because-
A. The heat is more evenly distributed inside the cooker.
B. A large flame is used.
C. Boiling point of water is elevated
D. Whole matter is converted into steam

Answer 1

Inside the cooker, the water is heated and eventually boils to steam. Since the pressure cooker is in a closed system, the steam cannot escape from there, so it collects over above the food. And as a result of this increases the pressure inside the cooker.

Complete answer:
The boiling point of a substance is the temperature at which the vapour pressure of a liquid is equal to the pressure surrounding the liquid and liquid changes to vapor. So the boiling point of a liquid varies depending upon the surrounding environmental pressure.
The normal boiling point or atmospheric boiling point of a liquid is the special case in which the vapor pressure of liquid equals the defined atmospheric pressure at sea level, that is one atmosphere. At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and allow bubbles of vapor to form inside the bulk of the liquid.
A liquid in a partial vacuum has a lower boiling point than when the liquid is at atmospheric pressure. A liquid at a higher pressure has a higher boiling point than when that liquid is at atmospheric pressure.
Cooking involves raising the temperature of food until chemical reactions take place, like break down of tough tissues or softens the starch present in the vegetable, and these types of reactions happen faster at high temperature.
When we normally cook the food, the temperature inside increases until water starts to boil. And at boiling point the temperature of the system will not increase, as the heat goes into boiling the water. But when we cook food inside the pressure cooker, the temperature at which water boils increases. Since we know the temperature at which water boils depends on the surrounding atmosphere’s pressure. Inside the pressure cooker the pressure increases, and since the surrounding pressure increases the boiling point temperature also increases. That means now the heat will increase the temperature of the system, rather than boiling the water. Since cooking reactions speed up at higher temperature, food cooks faster.

**Hence the correct option will be C.

Note:**
This is also the reason why cooking at high altitudes can be tricky. Air pressure decreases as we move higher above sea level. At lower pressure, water boils at lower temperature that means food will take much time to cook than normal. So at altitudes by raising the pressure and boiling point, the pressure cooker cooks the food at a faster rate.