Viscosity - 1 - GATE ME Fluid Mechanics Free MCQ Test with solutions

Explanation: According to the No-Slip condition, the relative velocity between the plate and the fluid in contact with it must be zero. Thus, the velocity of the fluid in contact with the upper plate is 0 and that with the lower plate is V.

Explanation: Viscosity is the internal friction of a fluid in motion. It is the property by the virtue of which the relative motion between two adjacent fluid layers is opposed.

Explanation: Viscosity is the property of a fluid and is constant for a given fluid under given conditions, irrespective of the fact whether the fluid is at rest or in motion.

Viscosity of a liquid is due to the cohesion between it’s molecules. With the increase in temperature of a liquid, cohesion increases, leading to the rise in viscosity. Viscosity of a gas is due to the momentum transfer between it’s molecules. With the increase in the temperature of a liquid, molecular motion increases, leading to the fall in viscosity.

Explanation: 
where F= viscous force, A= area, du ⁄ dx = velocity gradient, μ = co-effcient of viscosity. Therefore,

SI unit of μ is N-s/m² = Pa-s and CGS unit of μ is dyne-s/cm². 1 Poise= 1 dyne-s/cm² and 1 Stokes= 1 cm²/s. Thus, Stokes is not an unit of μ, rather it is a unit of kinematic viscosity υ.

Explanation: 
where F= viscous force, A= area, du ⁄ dx = velocity gradient, μ = co-effcient of viscosity. Therefore,

CGS unit of μ is = dyne-s/cm². 1 Poise= 1 dyne-s/cm² and 1 Stokes= 1 cm²/s. Thus, the CGS unit of μ will be Poise. Stokes is the CGS unit of kinematic viscosity.

Explanation:
1 Poise = 1 dyne-s/cm²  

Definition: Kinematic viscosity (ν) is defined as the ratio of dynamic viscosity (η) to density (ρ):

ν = η / ρ

Units:

• SI Unit: m²/s
• CGS Unit: Stokes (St), where 1 St = 1 cm²/s = 10⁻⁴ m²/s

Correct Answer is A: Stokes

Explanation: ν = μ/ρ, where ν = kinematic viscosity, μ = dynamic viscosity and ρ = density of the fluid.