something about......cooling and hot effects.................

Air Conditioning:

Bodily comfort depends on temperature as well as humidity. The comfortable conditions for an average person are ...............................................................................

(i) temperature between 23 and 25 °C, and 

(ii) relative humidity between 60 and 65 per cent. 

An air conditioner provides these conditions by regulating temperature and humidity.The cooling capacity of an A.C. is expressed in tons, e.g. 1 ton 2 ton etc. A 1 ton A.C. transfers 12000 BTU (British thermal unit) of heat from the room in an hour. (1 BTU = 1055 joule). Ton in this case has nothing to do with mass.

Refrigerator:

In a refrigerator, cooling is produced by the evaporation of a volatile liquid, FREON, inside a copper coil (evaporator), which surrounds the freezer. The vapor is removed and condensed to the liquid form in the condenser coil, fitted at the back of the cabinet, by a compression pump.

 The condenser coil becomes warm owing to the conversion of vapor into liquid inside it. From the condenser coil the liquid is sent back into the evaporator coil and the cycle goes on.A thermostat switch regulates the temperature inside the refrigerator by switching the pump on and off at intervals. In ordinary refrigerators, frost forms around the freezer coils. This frost not only decreases the inner capacity of the freezer, it also affects the cooling.

 In frost-free refrigerators, the freezer has three basic parts; a timer, a heating coil around the freezer coil and a temperature sensor periodically, the timer turns on the heating coil, which melts off the frost/ice. When the temperature rises to zero degree Celsius and all the ice is gone the temperature sensor turns off the heater coil.

Pressure Cooker: 

The boiling point of a liquid depends on external pressure.

When the atmospheric pressure is 76 cm of mercury water boils at 100°C. But when the pressure is increased, the boiling point of water is raised. For example, at a pressure of two atmospheres, water boils at 120°C. In a pressure cooker water boils at temperatures higher than 100 °C due to increased pressure. The increased boiling temperature allows water to hold more heat which cooks food faster.

At higher altitudes, atmospheric pressure is reduced.

This lowers the boiling point of water and food takes much longer to cook. Thus a pressure cooker becomes more essential for cooking on hill stations.