Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

What is a common instrument used to measure relative humidity?

1. Aneroid Barometer

2. Psychrometer

3. Thermometer

4. Anemometer

The correct answer is: Psychrometer

The psychrometer is a common instrument used to measure relative humidity because it operates on the principles of evaporation and temperature differences. A psychrometer typically consists of two thermometers: one measures the air temperature (the dry-bulb temperature), while the other has a wet cloth covering its bulb (the wet-bulb temperature). When air passes over the wet bulb, moisture evaporates from the cloth, which cools the wet-bulb thermometer. The difference in temperature readings between the two thermometers can then be used to calculate the relative humidity of the air using established tables or equations. This method of measuring relative humidity is effective because it directly relates to the air's moisture content and temperature. The ability to determine humidity levels is crucial in various fields such as meteorology, agriculture, and HVAC (heating, ventilation, and air conditioning) systems, where moisture control is essential for comfort and health. Other instruments mentioned, like the aneroid barometer, measure air pressure; the thermometer measures temperature; and the anemometer gauges wind speed. While they are important for weather understanding and analysis, they do not provide direct information about humidity levels in the air. Thus, the psychrometer is the most relevant choice for measuring relative humidity specifically.