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The liquid mainly used in a barometer is-

  1. Water
  2. Alcohol
  3. Mercury
  4. Barometer has no liquid inside it.

Answer (Detailed Solution Below)

Option 3 : Mercury
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Detailed Solution

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The correct answer is option 3) i.e. Mercury.

CONCEPT:

  • Barometer:  A barometer is an instrument that is used to measure atmospheric pressure in a particular environment.
  • Atmospheric pressure: It is the pressure exerted by a column of air of a unit surface area on the surface of the Earth.
  • Capillarity: It is the ability of a fluid to rise and fall in a capillary tube as a result of surface tension.

EXPLANATION:

  • Mercury is used inside a barometer.
  • Mercury is preferred over other liquids because of its high density.
  • The high density of mercury makes it expand less and thus rise to a reasonable height to measure atmospheric pressure.

Additional Information

  • Water and alcohol, if used inside a barometer,  will require almost 13.6 times larger barometer than a mercury barometer to measure the same pressure difference because of less density.
  • The vapour pressure of mercury is also low and hence does add to the measured atmospheric pressure thereby giving accurate measurement.
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