ANS:A - wet bulb temperature

The wet bulb temperature is a thermodynamic concept used in meteorology and engineering to measure the lowest temperature achievable by evaporative cooling of a liquid, typically water, in air. Here's how it works:

1. Wet Bulb Thermometer: To measure the wet bulb temperature, you use a thermometer with its bulb covered by a wet cloth or wick. When air flows over the wet cloth, evaporation occurs, which cools the bulb of the thermometer. This cooling effect depends on the rate of evaporation, which in turn depends on factors such as air temperature, humidity, and air movement.
2. Evaporative Cooling: Evaporation is a cooling process. When water evaporates from the wet cloth, it absorbs heat from the surrounding air, causing the air temperature to decrease. The rate of evaporation depends on how much moisture the air can hold, which is influenced by its temperature and humidity.
3. Equilibrium Temperature: The wet bulb temperature represents the temperature to which air will cool through evaporative cooling under specific conditions. It's an indicator of the cooling potential of the air. When air is unsaturated (relative humidity less than 100%), the wet bulb temperature is lower than the dry bulb temperature (the regular air temperature). However, when air is saturated (relative humidity 100%), the wet bulb temperature equals the dry bulb temperature because no further evaporation can occur.
4. Applications: Wet bulb temperature is crucial in various fields. In meteorology, it's used to determine the potential for thunderstorms, fog, and other weather phenomena. In engineering, particularly HVAC (heating, ventilation, and air conditioning), it helps assess the efficiency of cooling systems and determine the cooling capacity of air conditioning systems. It's also used in psychrometrics, the study of moist air, to analyze air conditioning processes and indoor air quality.