Which device uses both a dry and wet bulb thermometer to determine relative humidity?

The device that uses both a dry and wet bulb thermometer to determine relative humidity is the psychrometer. This instrument consists of two thermometers: one measures the air temperature (dry bulb) and the other is wrapped in a wet wick (wet bulb), from which moisture evaporates. The evaporation process cools the wet bulb thermometer, resulting in a lower temperature reading compared to the dry bulb.

To determine relative humidity, the readings from both thermometers are compared. The greater the difference between the two temperatures, the lower the humidity; conversely, a smaller difference indicates higher humidity. The psychrometric principles governing these readings allow for accurate calculations of relative humidity and are widely used in various applications, including HVAC systems and meteorology.

The other options do not serve this specific function; for example, a hygrometer also measures humidity, but it typically does not involve the use of both types of thermometers as the psychrometer does. A thermometer measures temperature alone and a barometer measures atmospheric pressure. Therefore, the psychrometer is uniquely identified by its dual thermometer setup specifically designed to gauge relative humidity.