Question

Give reasons for the following:
A. Doctor’s advice to put strips of wet cloth on the forehead of a person having high temperature.
B. Ice at 0 degree Celsius is more effective in cooling than water at 0 degree Celsius.

Answer 1

Hint: Latent heat is the heat given up or absorbed by a unit mass of a substance as it changes from a solid to a liquid, from a liquid to gas, or the reverse of either of these changes. It is related to a heat property known as enthalpy.

Complete step by step solution:
When strips of wet cloth are put on the forehead of a person having fever, the water in the cloth absorbs heat from the hot forehead to get vaporized.
It helps to decrease the extra heat in the body caused due to high fever consequently helps to reduce fever.
This depends on the fact that water in the process of evaporation takes away heat equivalent to latent heat from the patient’s body and thus lowers the temperature of his body.
Ice is more effective in cooling than water at the same temperature because ice can absorb latent heat as well as the heat energy in order to attain room temperature.
Water at 0 degree Celsius can absorb heat energy only to attain the room temperature. It has a high specific heat capacity so it stores more heat and is unable to cool things very easily at 0 degree and that is why we use ice because it has low specific heat which means that it stores less heat inside it.
Since, ice can absorb the latent heat form the environment; it has more cooling effectiveness as compared to water at same temperature.

Note: One cannot feel the latent heat; however the liquid can store all the latent heat. The only way to observe latent heat is when you try to transform the water back to ice. Heat energy is conserved no matter how the phase change occurs.