Question

When we switch on the fan in a closed room, the temperature of the air molecules :

• A. decreases
• B. increases
• C. remains unchanged
• D. may increase or decrease depending on the speed of rotation of the fan

Answer 1

Answer: (B)

We are given a closed room and the fan is switched on. In this case we assume that the room is insulated and hence no heat transfer happens through the walls, floor and there are no energy interactions with the surroundings.

The energy input of the room is the energy that the fan consumes from electric power. The energy drawn by the fan motor is converted to kinetic energy of air molecules present in the room which in turn converts into thermal energy and hence, there is an increase in the temperature of the air molecules in the room.