Question

The atmospheric pressure at sea level is ______ of Hg.
A. 76 km
B. 76 cm
C. 76 mm
D. 76 m

Answer 1

Hint: Barometer is a device used to measure atmospheric pressure at a place. It contains mercury and the scale is graduated in mm as mercury shows expansion or contractions only up to a few millimetres so we have a separate unit defined for barometer measurements.

Complete step-by-step answer:
Pressure is defined as the force applied on a surface per unit area. The expression for pressure is
$P = \dfrac{F}{A}$
There are many units used for pressure. The S.I. The unit of pressure is pascal (Pa). 1Pa=1 newton per square meter ($N/{m^2}$).
The dimensional formula of pressure is $\left[ {{M^1}{L^{ - 1}}{T^{ - 2}}} \right]$.
Atmospheric pressure is defined as the pressure exerted by the atmosphere due to its weight. It can be measured using a device called a barometer. In a barometer, there is a mercury column in which mercury moves up or down depending on atmospheric pressure at a place. It is graduated in millimetres and the unit used for measurements from a barometer is mm Hg.
1mm of Hg = 133.3224 Pa
All measurements from the barometer are made in this unit so the correct answer to our question is option C.
The atmospheric pressure at the sea level is 76mm of Hg.

Note: The atmospheric pressure is maximum at the sea level. The reason for this is that pressure decreases with increase in height in the atmosphere and atmospheric depth is maximum at the sea level. Under the sea level, pressure increases at greater speed because water exerts additional pressure and pressure increases by 1atm after every 10m depth under the sea level.