Understanding Measurement Instruments: Hygrometer and Barometer

The question asks us to complete an analogy based on the relationship between a measurement instrument and the quantity it measures. The first part of the analogy is "Hygrometer : Humidity". This tells us that a hygrometer is an instrument used to measure humidity.

Relationship Analysis: Hygrometer and Humidity

A hygrometer is specifically designed to measure the amount of water vapor present in the air, which is known as humidity. This instrument is commonly used in meteorology, HVAC systems, and various industrial applications where monitoring moisture levels is crucial.

Completing the Analogy: Barometer and Its Measurement

Following the pattern, we need to identify what a barometer measures. Let's examine the options provided:

• Current: This is the flow of electric charge, typically measured by an ammeter.
• Temperature: This is the degree of hotness or coldness, measured by a thermometer.
• Pressure: This is the force applied perpendicular to the surface of an object per unit area. Specifically, a barometer measures atmospheric pressure, which is the pressure exerted by the weight of the air in the atmosphere of Earth.
• Speed: This is the rate at which someone or something is able to move or operate. Linear speed is measured by a speedometer, while wind speed is measured by an anemometer.

Based on the function of a barometer, it measures pressure, particularly atmospheric pressure. Therefore, the relationship is Barometer : Pressure.

Conclusion on the Analogy

The analogy Hygrometer : Humidity :: Barometer : Pressure accurately reflects the instruments and the quantities they measure. The hygrometer measures humidity, and the barometer measures pressure.

Thus, the word that best completes the relationship is Pressure.

Revision Table: Instruments and Measurements

Additional Information on Measurement Concepts

Understanding different measurement instruments and the physical quantities they measure is fundamental in various fields like physics, meteorology, and engineering. Instruments like the hygrometer and barometer are vital for monitoring environmental conditions.

• Humidity is often expressed as relative humidity (percentage of maximum possible water vapor at a given temperature) or absolute humidity (mass of water vapor per unit volume of air).
• Atmospheric pressure varies with altitude and weather conditions. It is commonly measured in units like Pascals (Pa), hectopascals (hPa), millibars (mb), or inches of mercury (inHg). Standard atmospheric pressure at sea level is approximately $1013.25$ hPa or $1$ atmosphere (atm).
• Early barometers, like the mercury barometer, used the height of a column of mercury balanced by the weight of the atmosphere. Modern barometers often use aneroid mechanisms or electronic sensors.

Analogies like the one presented in the question help test the knowledge of these fundamental scientific relationships.