Physics Lesson 9.4.3 - Why is Mercury Used as Capillary Liquid in Barometers?

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Welcome to our Physics lesson on Why is Mercury Used as Capillary Liquid in Barometers?, this is the third lesson of our suite of physics lessons covering the topic of Gas Pressure, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.

Why is Mercury Used as Capillary Liquid in Barometers?

Mercury is a rare and expensive material. Also, it is very poisonous if consumed accidentally. Then, why it is used in barometers (and other pressure gauges we will discuss later)?

We will give answer to this question through the following exercise.

Example 2

Calculate the liquid's height inside the barometer column in normal atmospheric conditions if we use water as a capillary liquid instead of mercury. Density of water is 1000 kg/m³.

Solution 2

We know that the value of normal atmospheric pressure is 101 325 Pa. Thus, from the formula of liquid pressure, we can write

Now, it is clear why mercury is used in barometers despite its shortcomings. If we used another liquid such as water instead of mercury, we would need a 11 + meter high device. Such barometer would be inappropriate to carry and use in indoor conditions.

You have reached the end of Physics lesson 9.4.3 Why is Mercury Used as Capillary Liquid in Barometers?. There are 6 lessons in this physics tutorial covering Gas Pressure, you can access all the lessons from this tutorial below.

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2. Density and Pressure Physics tutorial: Gas Pressure. Read the Gas Pressure physics tutorial and build your physics knowledge of Density and Pressure
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6. Continuing learning density and pressure - read our next physics tutorial: Buoyancy. Archimedes' Principle

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