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    Question ID:   12821         Current Version: 1
Question: How does a hygrometer measure humidity?
Category: Science > Weather
Keywords: measure, humidity, hygrometer
Type: how
Rating:(0 ratings)    Views: 467    Discussions: 0   In Watch Lists: 1  

 
    Answer:
There are different types of hygrometers, so it depends on which type you are asking about.

A simple hygrometer used in classrooms that is made with a piece of hair and an attached arrow, works because on a damp day, the strand of hair will absorb the moisture from the air. This will make the hair stretch and so the arrow points lower. On a dry, sunny day the hair dries out and becomes shorter.

A whirling hygrometer, also called a sling psychrometer, measures relative humidity and temperature directly. It has two matched thermometers. One thermometer is called the dry bulb and the other the wet bulb. The wet bulb thermometer has a cotton sleeve wrapped around its base. Distilled water from a small reservoir is used to keep the sleeve wet. The hygrometer is whirled around in the air. While this happens, water from the sleeve of the wet bulb thermometer evaporates, and the wet-bulb temperature shown by the thermometer goes down.

Source: arm.gov

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