Question

What is $SI$ unit of viscosity coefficient $(\eta )$?

• A. pascal
• B. $Ns{m}^{-2}$
• C. $k{m}^{-2}s$
• D. $N{m}^{-2}$

Answer 1

Answer: (B)

Viscosity is defined as the ratio of the force required to shear a liquid to the velocity of shear (shear means when adjacent layers of liquid are made to slide over each other).
Coefficient of viscosity is defined as the tangential force required to maintain a unit velocity gradient between two parallel layers of liquid of unit area.

Coefficient of viscosity $=Fr/v$

$F=$ tangential force, Area,

$r=$ distance between the layers,

$v=$ velocity

so SI unit of the coefficient of viscosity is $N$ s $m^{-2}$