If an electric fan be switched on in a closed room, will the air of the room be cooled? If not, why do we feel cold?

Options

A. cooled
B. heated
C. maintains its temperature
D. heated or cooled depending on the atmospheric pressure

Explanation

To solve the question, we need to analyze the effects of an electric fan in a closed room and understand the concepts of air temperature and human sensation of coldness.

### Step-by-Step Solution:

1. **Understanding the Function of a Fan**:
- When an electric fan is switched on, it causes the blades to rotate, which in turn moves the air in the room.

**Hint**: Think about how a fan works and what it does to the air around it.

2. **Effect on Air Molecules**:
- The movement of the fan blades increases the kinetic energy of the air molecules. As the speed of the air molecules increases, they begin to vibrate more vigorously.

**Hint**: Consider how kinetic energy relates to temperature and molecular motion.

3. **Temperature Change**:
- The increased motion of the air molecules leads to an increase in the temperature of the air in the room. Therefore, the air does not cool down; instead, it becomes warmer.

**Hint**: Relate the concept of temperature to the average kinetic energy of the molecules.

4. **Human Sensation of Cold**:
- Although the air temperature increases, we feel cold because of the process of evaporation. When the air moves over our skin, it helps to evaporate sweat.

**Hint**: Think about how sweat evaporation affects body temperature.

5. **Evaporation and Cooling Effect**:
- The evaporation of sweat requires energy, which is taken from our body, leading to a cooling sensation. This is why we feel cold even when the air temperature is higher.

**Hint**: Consider the energy transfer involved in the phase change from liquid (sweat) to gas (water vapor).

### Final Conclusion:
- In summary, when an electric fan is switched on in a closed room, the air does not cool down; instead, it heats up due to increased molecular motion. However, we feel cold because the fan enhances the evaporation of sweat from our skin, which cools our body.

### Summary of Key Points:
1. The fan increases the speed of air molecules, raising the air temperature.
2. The sensation of coldness comes from the evaporation of sweat, which cools the body.