Question

Convection of heat takes place in:
(A) Metals only
(B) Liquids only
(C) Gases only
(D) Liquid and gases

Answer 1

Hint : To answer this question, we need to look into the basic definition of Convection. It is the phenomenon that causes the transfer of heat within matter. Then we have to find the required condition for this phenomenon to take place. Convection is the process of heat transfer by the bulk movement of molecules within fluids such as gases and liquids. The initial heat transfer between the object and the fluid takes place through conduction, but the bulk heat transfer happens due to the motion of the fluid.

Complete Step By Step Answer:
Convection is one of the phenomena which are responsible for the heat transfer within the matter. We know that there are three different modes of transfer of heat within the matter. These are conduction, convection, and radiation.
While the conduction is carried out as a result of the temperature difference between the two adjacent points in a matter, the radiation is carried by the electromagnetic waves. In both of these phenomena, there is no need for the matter itself to be moved for transferring the heat. But the convection is a phenomenon in which actual movement of the matter is involved. The part of the matter which is directly heated becomes light, and rises up and takes the place of the colder part of the matter. Then the colder part becomes heated and this cycle goes on. This way the heat transfer within the matter takes place.
So, convection can occur only in the matter which is capable of showing motion. The molecules of liquid and gases are not rigidly bound to each other and move freely. This makes the transfer of heat by convection possible.
Hence, the correct option is (D).

Note :
It should be remembered that convection does not take place in solids, because no movement of its constituent particles occurs. The liquids and the gases, collectively known as the fluids, have the capability of flowing. So, convection can take place in fluids. One of the most common examples of natural convection is the phenomena of the sea and land breeze.