Heat and Thermodynamics part-(1)

Food can be cooked faster in a pressure cooker since the boiling point of water increases with increase in pressure. As the water boils, the steam produced cannot evaporate so the pressure inside the cooker increases. The boiling point of water now becomes about 120°C. The load pin fixed on the heavy aluminum lid prevents any escape of steam. The rubber ring around the lid deals the liquid inside. Thus food gets cooked faster in a pressure cooker. Pressure cookers are more common in the mountains where elevation is high. At higher elevations, atmospheric pressure is lower and therefore water boils at lower temperature. In order to make up for that difference, people use pressure cookers.

Handle of pressure cookers is made up of ebonite because it is an insulator and prevents heat from reaching the handle and prevents burning of hands. Ebonite is a strong material. So assertion (A) and reason (R) both are correct but R is not the correct explanation of A

In a pressure cooker the food is cooked with the boiling of water. Boiling point is increased inside a pressure cooker by increasing the pressure. This pressure can be adjusted by changing the weight placed on the top of the cooker lid. The pressure (and cooking temperature) also depends upon area of the hole in the lid. The principle of pressure cooking is to maintain a temperature of about 120°C inside the cooker as opposed to a temperature of 100°C attained in open vessels. The weight is designed in such a way that it will kick when the pressure inside just exceeds about one atmospheric gauge thereby releasing the excess pressure. This is the pressure at which the boiling point is about 120°C. Once the requisite pressure and temperature is attained, more heat input (by increasing the temperature of the flame) results in more steam generated which is released through the lid and hence the cooking temperature remains the same, which is about 120°C. Thus, temperature at which the food is cooked does not depend upon temperature of the flame.

In a pressure cooker the food is cooked with the boiling of water. Boiling point is increased inside a pressure cooker by increasing the pressure. This pressure can be adjusted by changing the weight placed on the top of the cooker lid. The pressure (and cooking temperature) also depends upon area of the hole in the lid. The principle of pressure cooking is to maintain a temperature of about 120°C inside the cooker as opposed to a temperature of 100°C attained in open vessels. The weight is designed in such a way that it will kick when the pressure inside just exceeds about one atmospheric gauge thereby releasing the excess pressure. This is the pressure at which the boiling point is about 120°C. Once the requisite pressure and temperature is attained, more heat input (by increasing the temperature of the flame) results in more steam generated which is released through the lid and hence the cooking temperature remains the same, which is about 120°C. Thus, temperature at which the food is cooked does not depend upon temperature of the flame.

Steam at 100 degree celsius contains 540 calorie more than the boiling water at the same temperature due to the latent of heat vaporization the letent heat of fusion of ice is 80 cal/gm thus the statement 1 and 2 are incorrect while the statement 3 is correct in an air conditioner heat is extracted from the room air at the evaporator coil and is ejected out at the condenser coil.

A glass bottle containing water breaks down when kept in freezer because the frozen water will have more than than the liquid water so increased volume will put pressure on the walls of the bottle and it will break.

A glass bottle containing water breaks down when kept in freezer because the frozen water will have more than than the liquid water so increased volume will put pressure on the walls of the bottle and it will break.

when an ice cube melts in a glass of water the water level does not changed as the melted water will occupy exactly the same amount of space as the ice under the water level previously occupied

when you have cloudy night the clouds prevent heat from escaping through the atmosphere and into space the clouds act like a blanket and trap the heat.That is why every time when there is a cloudy night it is always warmer than a clear night.

The cloud nights warmer than the clear night because the clouds prevent radiation of heat from the ground and the air and they reflect back the heat.