Relative humidity can be measured with which instrument?

Relative humidity can be measured with which instrument?

• A. Barometer
• B. Anemometer
• C. Thermometer
• D. Psychrometer

Answer: (D)

Relative humidity is determined by how much water vapor is in the air relative to what the air can hold at a given temperature. A psychrometer does this by using two thermometers: a dry-bulb thermometer that reads the ambient air temperature and a wet-bulb thermometer with a wick saturated in water. As air moves over the wet wick, evaporation occurs, which cools the wet-bulb thermometer. The rate of this cooling depends on how much moisture is already in the air—the drier the air, the more the wet bulb cools, creating a larger difference between the two readings; the more humid the air, the smaller the difference. Those two temperature readings are then used (often with a psychrometric chart or calculation) to determine the relative humidity. Other instruments mentioned measure different quantities: a barometer gauges air pressure, an anemometer measures wind speed, and a thermometer measures temperature.

Relative humidity is determined by how much water vapor is in the air relative to what the air can hold at a given temperature. A psychrometer does this by using two thermometers: a dry-bulb thermometer that reads the ambient air temperature and a wet-bulb thermometer with a wick saturated in water. As air moves over the wet wick, evaporation occurs, which cools the wet-bulb thermometer. The rate of this cooling depends on how much moisture is already in the air—the drier the air, the more the wet bulb cools, creating a larger difference between the two readings; the more humid the air, the smaller the difference. Those two temperature readings are then used (often with a psychrometric chart or calculation) to determine the relative humidity. Other instruments mentioned measure different quantities: a barometer gauges air pressure, an anemometer measures wind speed, and a thermometer measures temperature.