Question

Write answers to the following question.

(a) How does a fever get lowered by putting a cold compress on the forehead of a patient ?
(b) Why are the houses in Rajasthan painted white ?
(c) What are the modes of heat transfer ?
(d) Explain which mode of heat transfer causes sea breezes and land breezes.
(e) Why is the outer coat of the penguins of Antarctica black ?
(f) Why are heaters fitted near the floor and air conditioners, near the ceiling of a room ?

Answer 1

(a) Cold compress is made up of material that absorbs heats. Thus, by putting it on the forehead of a patient suffering from high fever, the heat flow takes place from the head of the patient to the cold compress. Therefore, the cold compress absorbs heat from the patient's body and lowers the body temperature.

(b) White colours are reflectors of heat. Thus, Rajasthan, a very hot city, has houses with their walls painted white so that most of heat from the Sun is reflected back to the atmosphere. This keeps the houses cool from inside.

(c) There are three modes of heat transfer:

• Conduction: Conduction is a process in which heat is transferred from the hotter end of an object to its cooler end.
• Convection: The process of transference of heat through a fluid (liquid or gas) is called convection.
• Radiation: Radiation is a method of heat transfer which does not require a medium.

(d) Convection causes sea breeze and land breeze. Heat transfer through fluids takes place by the process of convection.
Sea breeze: It is the wind that blows from the sea or the oceans towards the land. It develops during day time when the land heats up quickly. Also, the water heats up slowly as compared to land due to which water in the sea and oceans is relatively cooler than land. Therefore, the air near the land becomes hot and rises up and the cold air from sea takes the place of hot air. The hot air than moves toward the sea to complete the cycle.

Land breeze: It is the wind that blows from the land towards the sea or the oceans. It develops during night time. Land cools down faster than water. Therefore, during night time, land is cooler than sea. Hence, cool air from the land blows towards the sea. This is called the land breeze.

(e) Black colour is good absorbers or trappers of heat. So, in cold regions like Antarctica, the black outer coating of Penguins helps them to absorb as much heat from the surrounding and keep their bodies warm.

(f) Room heaters are fitted near the floor because this allows the hot air near the heater to rise up and warm the entire room.
The air conditioners are fitted near the ceiling, so that the cold air from the AC takes the place of hot air rising up from the bottom. In this way, the entire room gets cooled.