Describe how a sling psychrometer can be used to determine the relative humidity or dew point

Question

What will be an ideal response?

Answer 1

ANSWER: An appropriate answer would be that the psychrometer is a common instrument used to obtain dew point and relative humidity. It consists of two liquid-in-glass thermometers mounted side by side and attached to a piece of metal that has either a handle or chain at one end. The thermometers are exactly alike except that one has a piece of cloth (wick) covering the bulb. The wick-covered thermometer—called the wet bulb—is dipped in clean (usually distilled) water, while the other thermometer is kept dry. In a sling psychrometer both thermometers are ventilated for a few minutes by whirling the instrument. Water evaporates from the wick and the thermometer cools. The drier the air, the greater the amount of evaporation and cooling. After a few minutes, the wick- covered thermometer will cool to the lowest value possible.
The dry thermometer (commonly called the dry bulb) gives the current air temperature, or dry-bulb temperature. The temperature difference between the dry bulb and the wet bulb is known as the wet-bulb depression. A large depression indicates that a great deal of water can evaporate into the air and that the relative humidity is low. A small depression indicates that little evaporation of water vapor is possible, so the air is close to saturation and the relative humidity is high. If there is no depression, the dry bulb, the wet bulb, and the dew point are the same; the air is saturated and the relative humidity is 100 percent.