Beginner Topic 225 of 1102 States of Matter & Solutions
Barometer
An instrument measuring atmospheric pressure, standard value 760 mmHg or 101.325 kPa.
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In-depth explanation of Barometer
A barometer is an instrument that measures atmospheric pressure by balancing it against the weight of a liquid column. Torricelli invented the mercury barometer in 1643 by inverting a mercury-filled glass tube in a dish of mercury. The mercury column stands at about 760 mm at sea level because atmospheric pressure supports exactly that height. A water barometer would need a column about 10.3 m tall for the same pressure, which is why mercury is used. Atmospheric pressure decreases with altitude because there is less air above, so the column drops when the barometer is carried up a mountain.
Going deeper: Barometer
Key ideas: Hydrostatic balance gives P_atm = rho g h. With mercury, rho = 13595 kg/m3, g = 9.81 m/s2 and h = 0.760 m, the result is about 101.3 kPa. Atmospheric pressure falls about 12 percent per kilometre near sea level, roughly 1 mmHg per 11 m of climb. Aneroid barometers use a flexing metal capsule instead of liquid.
Common mistakes and connections: Tilting the tube or using a wider tube does not change the vertical height of the column. Another error is thinking the vacuum above mercury pulls the liquid up; the atmosphere pushes it. Mercury vapour is negligible in that space but toxic. Links to pressure units, boiling point at altitude and weather prediction.
Visualization of Barometer
A barometer balances air pressure against a liquid column: mercury rises 760 mm at 1 atm, while water would need a 10.3 m tube. The interactive lesson shows this as a live animation or chart.
Worked example and use case
At the top of Mount Everest, about 8850 m high, the atmospheric pressure is roughly one third of its sea-level value.
Frequently asked questions about Barometer
What is Barometer?
An instrument measuring atmospheric pressure, standard value 760 mmHg or 101.325 kPa.
Is Barometer a beginner, intermediate or advanced topic?
Barometer is a beginner topic in States of Matter & Solutions. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Barometer?
Study these earlier topics in States of Matter & Solutions first: Plasma, Bose-Einstein Condensate, Pressure.
What comes after Barometer?
The next topics in States of Matter & Solutions are Standard Temperature and Pressure and Boyle's Law.
Can I practise Barometer with quizzes?
Yes. The interactive lesson includes a self-check question on Barometer, and the States of Matter & Solutions quiz draws on every topic in this area.
Where Barometer fits in States of Matter & Solutions
Barometer is topic 6 of 109 in States of Matter & Solutions.