Stokes Law is Valid for Particle Size?

By BYJU'S Exam Prep

Updated on: September 25th, 2023

Stokes law is valid for particle size

  1. Less than 0.002mm
  2. Greater than 0.2m
  3. Between 0.002mm to 0.2mm
  4. Less than 0.02mm and greater than 0.2mm

Answer: C. Between 0.002mm to 0.2mm

Stokes’s law is valid for particle size between 0.002mm to 0.2mm.


Stokes law states that the force resisting a spherical body is a viscous fluid is directly proportional to the velocity of the sphere, the radius of the sphere and the viscosity of the fluid.

Settling Velocity by stokes law is given by:

V = gd2(ps-pw)/18μ


V = Velocity of settling particle

D = Diameter of settling particle

g = Acceleration due to gravity

ps = Density of settling particle

p= Density of water

μ = Dynamic viscosity of fluid

Stokes law is valid for particle size between 0.002mm to 0.2mm and upto a maximum Reynold’s number of 1.

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