What is the difference between the natural wet-bulb temperature and dry-bulb temperature?

• A. They are interchangeable and always equal in humid environments.
• B. Wet-bulb measures humidity only, while dry-bulb is the ambient air temperature.
• C. The natural wet-bulb accounts for evaporative cooling (moisture effects) in the environment, while dry-bulb is the ambient air temperature without moisture consideration.
• D. Wet-bulb is always higher than dry-bulb by a fixed amount.

Answer: (C)

The main idea is that temperature readings can be influenced by moisture through evaporative cooling. The dry-bulb temperature is simply the ambient air temperature measured by a standard thermometer with a dry sensor. The natural wet-bulb temperature, on the other hand, uses a wetted wick or surface so that evaporation can occur as air moves past it. As water evaporates, it absorbs latent heat from the surroundings, cooling the thermometer. This means the wet-bulb reading reflects not just the air temperature but also how much moisture is in the air and the potential for evaporative cooling.

Because evaporation depends on humidity and air movement, the wet-bulb temperature is typically lower than the dry-bulb temperature in dry or moderately moist air and only approaches the dry-bulb when the air is fully saturated (100% relative humidity). So the wet-bulb temperature accounts for moisture effects, while the dry-bulb temperature does not.

That’s why the correct description is that the natural wet-bulb accounts for evaporative cooling (moisture effects) in the environment, whereas the dry-bulb is the ambient air temperature without moisture consideration.