Correct Answer - Option 2 : Practically independent of variation of pressure
Concept:
When two adjacent layers of fluid are in relative motion, they resist the motion of each other such fundamental property of fluids is called viscosity.
The cause of dynamic viscosity in gasses is different than that of liquid.
In liquids, the cause of dynamic viscosity is intermolecular force of attraction or also called cohesive forces and on increasing the temperature molecules of liquids tries to move away from each other which in turn reduces the cohesive force and hence, dynamic viscosity decreases with increase in temperature in case of liquids.
In case of gasses, the cause of dynamic viscosity is randomness of molecules and on increasing the temperature, the randomness among molecules increases and hence, dynamic viscosity increases with increase in temperature of gasses.
The pressure has no effect on dynamic viscosity of liquid or gasses, because it was experimentally found that by decreasing or increasing the pressure neither cohesive force changes nor randomness of molecules got affected.
Kinematic viscosity
kinematic viscosity is the ratio of dynamic viscosity and density of liquid.
\(\nu=\frac{\mu}{\rho}\)
⇒ μ for air increases with the rise in temperature and ρ decreases with rise in temperature so the value of kinematic viscosity increases.
