Physics 2002 JAMB Past Questions - Question 20: Blowing air over a liquid aids evaporation by

Correct Answer

D

Explanation

Blowing air over a liquid aids evaporation by increasing the rate of evaporation through several mechanisms:

1. Increased Surface Area: When you blow air over a liquid, it creates turbulence and increases the surface area of the liquid that is exposed to the air. This increased surface area allows more liquid molecules to come into contact with the air, which promotes faster evaporation.

2. Breaks Boundary Layer: A thin layer of air, known as the boundary layer, forms on the surface of the liquid. This layer can slow down evaporation because it can become saturated with water vapor. Blowing air disrupts this boundary layer, ensuring that fresh, dry air continuously comes into contact with the liquid, facilitating quicker evaporation.

3. Heat Transfer: As air moves over the liquid, it can carry away heat from the liquid's surface. Evaporation is an endothermic process that requires heat energy to break the intermolecular bonds of the liquid molecules and convert them into vapor. The movement of air helps maintain a temperature difference between the liquid surface and the surroundings, promoting faster evaporation.

4. Enhanced Mixing: Blowing air over the liquid also helps in mixing the air and the vapor, preventing the buildup of vapor concentration near the liquid's surface. This promotes efficient evaporation by maintaining a concentration gradient that encourages the movement of water molecules from the liquid to the gas phase.

In various industrial and everyday applications, such as drying processes, cooling systems, and even in everyday activities like using fans to dry wet clothing, blowing air over a liquid is employed to accelerate the evaporation process.