Question

(i) What is evaporation?
(ii) State any three factors that affect evaporation.
(iii) Why does a desert cooler cool better on a dry and hot
day?
[5 Marks]

Answer 1

(i) The phenomenon of change of a liquid into its
vapour state at any temperature below its boiling
point is called evaporation.
[1 Mark]
(ii) The three factors affecting evaporation are:

• Temperature: Increase in temperature promotes evaporation as liquid particles gain more energy and vapourise easily.

[1 Mark]

• Humidity: Increase in humidity reduces the rate of evaporation as air is already saturated with moisture.

[1 Mark]

• Increase in surface area of the liquid increases the rate of evaporation as more number of particles are present on the surface and can vapourise quickly on gaining sufficient energy.

[1 Mark]

(iii) A desert cooler cools better on a dry and hot
day because on a dry and hot day the
temperature is high and humidity is less, which
together increase the rate of evaporation
resulting in better cooling.
[1 Mark]