Question

State the SI unit of pressure.
A. Newton
B. Pascal
C. Coulomb
D. Copernicus

Answer 1

Hint: The definition of pressure is force applied per unit area. Hence, its units must have the dimensions of force per area. By following this thought process and a bit of option elimination, one can reach at the correct answer.

Complete step by step answer:
Pressure applied on or by a body is defined as the force exerted per unit area on a surface.
Therefore,
$\text{Pressure = }\dfrac{\text{Force}}{\text{Area}}$.
Hence, the units of pressure must have the same units as the ratio of the physical quantities of force to area.
For, finding out the SI unit, it is important to write the SI units of force and area.
The SI unit of force is Newton $\left( N \right)$ and the SI unit of area is meter-squared $\left( {{m}^{2}} \right)$ since area has the dimensions of length squared and the SI unit of length is meter$\left( m \right)$.
Therefore, the SI unit of pressure will be $\dfrac{N}{{{m}^{2}}}=N{{m}^{-2}}$.
$N{{m}^{-2}}$ is also known as Pascal $\left( Pa \right)$after the French physicist and mathematician Blaise Pascal.
One Pascal is equal to one Newton per meter squared. That is,
$1Pa=\dfrac{1N}{1{{m}^{2}}}$ .
Hence, the correct option is B) Pascal.
Additional information: There is also another unit of pressure known as atmospheric pressure or$atm$. One atmospheric pressure is the pressure of the atmosphere at sea level. It is related to the Pascal by the mathematical relation
$1atm=1.01325\times {{10}^{5}}Pa$

Note: Though the SI system of units is the universally accepted system of units for all scientific purposes, still students must know a little about some important units of other systems and their conversions to the SI system. This sometimes comes in very handy as sometimes questions are set on purpose using units of other systems such as the CGS or FPS systems to check the students’ knowledge of these conversions. If the student does not know the conversion, he will not be able to proceed with the question at all.
For example, an important unit in the CGS system is the $dyne/c{{m}^{2}}$ which is the unit of pressure, where $1dyne=0.1Pa$.