Which device uses the principle of wet-bulb and dry-bulb thermometers to measure humidity?

The device that utilizes the principle of wet-bulb and dry-bulb thermometers to measure humidity is a hygrometer. This instrument specifically uses the differences in temperature readings between the wet-bulb and dry-bulb thermometers to calculate the relative humidity of the air.

The dry-bulb thermometer measures the air temperature, while the wet-bulb thermometer is kept moist and measures the temperature through the cooling effect of evaporation. The evaporative cooling is influenced by the humidity level in the air; therefore, by analyzing the temperature difference between the two thermometers, one can accurately derive relative humidity values.

This method provides a reliable measure of humidity, which is crucial in various fields, including meteorology, agriculture, and HVAC systems. The other devices listed, such as a pyranometer (which measures solar radiation), a thermometer (which measures temperature), and a hydrometer (which measures the specific gravity of liquids), do not serve the purpose of measuring humidity directly.