How is relative humidity measured?

Relative humidity is measured using the wet bulb and dry bulb thermometers, which are part of a psychrometer setup. The dry bulb thermometer measures the air temperature, while the wet bulb thermometer has a wick that is moistened. When air passes over the wet bulb, evaporation occurs, which cools the thermometer. The difference in temperature readings between the dry bulb and the wet bulb thermometers is correlated to the moisture content of the air, allowing for the calculation of relative humidity.

The key to understanding this method lies in the principle of evaporation and temperature decrease. The greater the difference between the dry bulb and wet bulb readings, the lower the relative humidity, as less moisture is available in the air to facilitate evaporation. Conversely, if the relative humidity is high, the difference will be smaller, indicating that the air is already holding a significant amount of moisture.

This method is widely used because it provides a direct measurement that can be easily converted into relative humidity values. Other options presented do not utilize the correct combination of thermometers required for accurate measurement of relative humidity.