### Theory:

Convection:
When we heat the water in the vessel, water molecules at the bottom receive heat energy and move upward. Then the molecules at the top come down and get heated. This mode of heat transfer is called as convection. Air in the atmosphere also follows the same principle while heating. Thus, the form of heat transfer from regions of higher temperature to areas of lower temperature by the actual movement of molecules is called convection. Convection takes place in liquids and gases.

Convection is defined as the movement of fluid (liquid and gasmolecules from higher temperature regions to lower temperature regions.

Fig. - Convection

Fig. - Convection process

Example:
The following are some examples of convection in daily life.
• Boiling of water - The molecules with a high density move at the bottom (Cold water). In contrast, the molecules with less dense (Hot water) move upwards, resulting in the circular motion of the molecules so that water gets heated.
• The formation of land breeze and sea breeze is due to convection of the air.
• Wind flows from one region to another region by convection.
• In warm-blooded animals, blood circulation takes place with the help of convection which helps to maintain the body temperature.
• In hot air balloons, heat is transferred by convection, and so the balloon raises.
• In refrigerators, cool air moves downward and replaces the hot air because of convection.
Note: Heat transfer by radiation is visible to our eyes. When a substance is heated to $$500$$°C, the radiation becomes visible to the eye as a dull red glow, and the skin is sensing the warmth. Further heating rapidly increases the amount of radiation, and its perceived colour becomes orange, yellow and finally white.