Question

Which of the following explains heat transfer by convection?

• A. When a substance is heated, molecules absorb heat energy and vibrate. When neighbouring molecules collide, energy is transmitted through the material.
• B. When a substance is heated, molecules absorb heat energy and substance expands. Due to this, density of heated molecules decreases and so they rise upwards taking the heat energy along with them
• C. Heat radiation is transmitted with the help of waves.
• D. None of the above

Answer 1

The correct option is B When a substance is heated, molecules absorb heat energy and substance expands. Due to this, density of heated molecules decreases and so they rise upwards taking the heat energy along with them

Convection is the dominant mechanism of heat flow in fluids. In convection, heat supplied is absorbed by the molecules and the material expands. As this happens, density decreases and heated part of the material begins to move upwards. During the process, heat is transferred by actual motion of the molecules from one place to another.