RAS question
Which instrument is used to measure atmospheric pressure?
Correct answer: (C) Barometer.
A barometer is the instrument used to measure atmospheric pressure.
Explanation
A barometer measures atmospheric pressure, so option C is the right answer. NCERT explains atmospheric pressure as the pressure due to the weight of the air column above a point; at sea level it is 1 atm, about 1.013 x 10^5 Pa. The cited NCERT chapter also describes Evangelista Torricelli's method for measuring this pressure: a mercury-filled glass tube inverted into a mercury trough, known as a mercury barometer. In that device, atmospheric pressure balances a mercury column of about 76 cm at sea level, which is why atmospheric pressure is also commonly expressed as 760 mm Hg. The other instruments listed measure temperature, humidity, or wind speed, not air pressure.
Why the other options are wrong
- (A) A thermometer measures temperature, whereas the question asks for the instrument used to measure atmospheric pressure.
- (B) A hygrometer measures humidity, so it does not measure the pressure exerted by the atmosphere.
- (D) An anemometer measures wind speed, not the atmospheric pressure balanced in a barometer.
Concept
This tests the basic physics and geography concept of atmospheric pressure and its measurement. It recurs in RAS because pressure, winds, weather systems, and standard physical units are linked across general science and physical geography.