Question

Account for the following
a. Water coolers are not effective on a rainy day.
b. After a hot sunny day people sprinkle water on the roof or open ground.
c. Evaporation produces cooling.
d. A rubber band is considered as a solid. Give reason.

Answer 1

1. Water coolers are not effective in rainy days as humidity is very high during rainy days. When we fill water in coolers. the dry grass on the 3 sides gets wet and then at these dry grass the process of evaporation takes place, that cools the area around and we get cool air. However, when the humidity is high rate of evaporation is very slow. So, there is no longer cooling of grass.

2. After a hot sunny day people sprinkle water on hot roofs to cool the surface. When we sprinkle water on the hot roof, it absorbs the heat from the hot surface and evaporates, thereby causing a cooling effect on the roof.

3. Evaporation is the process in which water is converted to vapour at normal temperatures. In this process, the tiny particles of water at the surface absorbs the heat energy from the surroundings and cool it, leaving the surface in the form of vapours.

4. Rubber band is a solid as it does not flow (no fluidity) and it changes shape only under the effect of external force.