Question

The SI unit of atmospheric pressure is _______.
A. Barye
B. Pascal
C. Dyne
D. None of the above

Answer 1

Hint: Pressure applied on a body is the normal force exerted on it per unit surface area. Therefore, essentially, pressure is the ratio of the total force applied to the total surface area of the object. Therefore, it must have units that represent this ratio. Atmospheric pressure is the term given to the pressure exerted by the atmosphere at a place.

Formula used:
$\text{Pressure = }{\displaystyle \frac{\text{Force}}{\text{Area}}}$

Complete step by step answer:
Pressure is a physical quantity that is defined as the force per unit surface area acting normal to the surface, exerted on a body. That is, pressure is the ratio of the total force normal to a surface to the total surface area of the surface. Hence,
 $\text{Pressure = }{\displaystyle \frac{\text{Force}}{\text{Area}}}$
Therefore, the SI units of pressure can be found out by writing the SI units of force and area respectively in the appropriate ratio.
The SI unit of force is $\text{Newton }\left(N\right)$ and the SI unit of area is $\text{metre-squared}\left(m^2\right)$.
Hence, the SI unit of pressure is ${\displaystyle \frac{N}{m^2}}=N.m^{-2}$.
This unit is also known as $\text{Pascal}\left(Pa\right)$, with the relation being
$1Pa=1N.m^{-2}$.
Atmospheric pressure is nothing but the term given to the pressure applied by the atmosphere on an object at a specific location. Therefore, it also has the units of pressure, that is, $\text{Pascal}\left(Pa\right)$.
Therefore, the correct option is B) Pascal.

Note: Students may have heard of the unit atmosphere$\left(atm\right)$ for pressure and think that it is the SI unit for atmospheric pressure. That is not true, since ‘one atmosphere’ is not an SI unit of pressure. It is the pressure exerted by the atmosphere on an object at sea level.
$1atm=1.01325\times {10}^{5}Pa$
There are also other units for pressure such as torr and bar. However, they are all derived by some mathematical relations from the SI unit $\text{Pascal}\left(Pa\right)$.