Question

The air becomes heated by
A. Conduction
B. Convection
C. Radiation
D. Expansion
E. Diffusion

Answer 1

According to thermodynamics any matter which is made up of atoms and molecules can transfer heat. Heat transfer can be defined as the phenomenon that conveys energy and entropy from one location to another.

Complete step by step solution:
As solids transfer heat energy by the method of conduction, liquids and gases transfer heat energy through convection. So the method by which the air gets heated up is called convection.

Therefore the correct option is B.

Additional Information:
Let us know how convection takes place. When we have a source of heat energy in the air, the air molecules just above the source will get heated up quickly. As a result of this, the air molecules expand and this makes them less dense than the surrounding air molecules. The lighter air molecules will always move up. Now to replace the warmer air molecules that moved upwards cooler air molecules will take their place. This cycle keeps repeating itself.
We can see this process of convection in the real-life example as land and sea breeze. In the daytime land near the sea will be hotter than the sea. The surface of the sea will be cool. During a hot day, the air above the land gets hotter. The air molecules will expand and move upward. To fill the vacancy of air molecules above the ground air molecules above the surface of the sea, that is the cooler air comes rushing towards the land. Now the warmer air molecules will move towards the sea to complete this cycle. The air from the sea is called the sea breeze and the air from the land is called the land breeze.
This is how convection takes place.

Note:
The heat transfer takes place not only by convection but there are also by some other methods in which the heat is transferred in the surrounding. They are conduction and radiation. So including convection, there are three traditional ways of heat transfer. Conduction is the process in which the heat is transferred from the object of higher temperature to the object of lower temperature. Random motion of molecules will result in radiation. Heat transferred through radiation is measured using a device known as a thermocouple.