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Barometer
Beginner
Measures atmospheric pressure with a mercury column.
P = ρghA mercury barometer balances atmospheric pressure with a column of height h = P/ρg ≈ 760 mm. Changes in height indicate weather changes.
With water the column would be 10.3 m.
The tube cross-section doesn't matter.
In more detail
A barometer measures atmospheric pressure by balancing the air's pressure against a column of liquid, often mercury. The height of the column gives the pressure.
Real-world uses
- Mercury barometers were the standard instrument for measuring pressure.
- Aneroid barometers in homes use a sealed metal capsule instead of liquid.
- A mercury barometer in a laboratory measures air pressure by the height of a column of mercury it supports.
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Frequently asked questions
Why is mercury used?
It is dense, so the column needed is short and manageable.
Why is the mercury column about 760 mm?
Because at sea level, atmospheric pressure balances about 760 mm of mercury.
Why is mercury used in barometers?
It is very dense, so the column needed to balance atmospheric pressure is a manageable height of about 76 cm.
Related topics in Fluids & Elasticity
Pascal's law · Hydraulic press · Atmospheric pressure · Manometer · Gauge and absolute pressure · Buoyancy