In meteorology and experimental physics, humidity (the amount of water vapour present in air) is measured using which one of the following instruments?

Introduction / Context:

Humidity is an important parameter in weather forecasting, comfort studies, and many industrial processes. It measures the amount of water vapour present in the air. Several instruments are used in meteorology and environmental monitoring, each with a specific purpose. This question asks you to identify the instrument whose primary function is to measure humidity.

Given Data / Assumptions:

• Humidity refers to the water vapour content of air, often expressed as relative humidity.
• We consider common instruments: hydrometer, hygrometer, psychrometer and anemometer.
• Only one of these is the general name for instruments that measure humidity directly.

Concept / Approach:

The term hygrometer is used for instruments designed to measure humidity. There are several types of hygrometers, including hair hygrometers, electronic capacitance hygrometers and psychrometers. A psychrometer is a specific type of hygrometer that uses the difference between wet bulb and dry bulb thermometer readings to determine humidity. Hydrometers, on the other hand, measure the relative density or specific gravity of liquids, not humidity. Anemometers measure wind speed. Thus, the general answer to which device measures humidity is hygrometer.

Step-by-Step Solution:

Verification / Alternative check:

Weather stations often report humidity measured by electronic hygrometers or psychrometers. The instrument manuals and meteorology textbooks refer to these devices as hygrometers. Hydrometers are found in laboratories and industries handling liquids, not air humidity. Anemometers are mounted on masts for wind measurement, not for moisture content, confirming the identification.

Why Other Options Are Wrong:

Option A: Hydrometer is for liquid density, not for atmospheric humidity.

Option C: Psychrometer is indeed used to determine humidity but is specifically a type of hygrometer using two thermometers. In many exam questions, the standard and more general term sought is hygrometer.

Option D: Anemometer measures wind speed, not humidity.

Common Pitfalls:

Students may confuse hydrometer and hygrometer because their names sound similar. Remember that hydro relates to liquid water and density, while hygro relates to moisture or humidity. Also, some texts emphasise psychrometers, which can cause confusion. Keeping clear associations hydrometer with liquids, hygrometer with humidity, and anemometer with wind helps avoid these mistakes.

Final Answer:

The instrument used to measure humidity is the Hygrometer.