1. Viscosity is a property of a fluid that offers resistance to:
a) Change in pressure
b) Change in temperature
c) Flow and deformation under shear stress
d) Change in volume
Answer: c) Flow and deformation under shear stress
Explanation: Viscosity is the measure of a fluid’s internal resistance to flow. It quantifies the friction between adjacent layers of fluid moving at different velocities.
2. The SI unit of dynamic viscosity is:
a) Stokes
b) Poise
c) Pascal-second (Pa·s)
d) Newton
Answer: c) Pascal-second (Pa·s)
Explanation: The SI derived unit for dynamic viscosity is Pascal-second (Pa·s), which is equivalent to N·s/m² or kg/(m·s).
3. The CGS unit of dynamic viscosity is:
a) Stokes
b) Poise
c) Pascal
d) Dyne
Answer: b) Poise
Explanation: The CGS unit is Poise (P), named after Jean Léonard Marie Poiseuille. 1 Poise = 0.1 Pa·s.
4. The unit of kinematic viscosity is:
a) Poise
b) Pascal-second
c) Stokes
d) Poiseuille
Answer: c) Stokes
Explanation: Kinematic viscosity (ν) is the ratio of dynamic viscosity (μ) to density (ρ). Its CGS unit is Stokes (St). SI unit is m²/s.
5. Which of the following fluids has the highest viscosity?
a) Water
b) Air
c) Honey
d) Kerosene
Answer: c) Honey
Explanation: Honey is a thick, sticky fluid with strong internal friction, giving it a much higher viscosity than water, kerosene, or air.
6. Viscosity in fluids arises primarily due to:
a) Gravitational forces
b) Adhesive forces
c) Intermolecular forces and momentum transfer
d) Surface tension
Answer: c) Intermolecular forces and momentum transfer
Explanation: The resistance (viscosity) comes from the cohesive forces between molecules in a liquid and the molecular momentum exchange in gases.
7. The relationship between dynamic viscosity (µ) and kinematic viscosity (ν) is given by:
a) ν = µ / ρ
b) µ = ν / ρ
c) ρ = µ / ν
d) ν = µ * ρ
Answer: a) ν = µ / ρ
Explanation: By definition, kinematic viscosity (ν) is the dynamic viscosity (µ) divided by the density (ρ) of the fluid.
8. A fluid that has no viscosity is called:
a) Real fluid
b) Ideal fluid
c) Newtonian fluid
d) Pseudoplastic fluid
Answer: b) Ideal fluid
Explanation: An ideal fluid is a hypothetical fluid that is assumed to have zero viscosity and incompressibility for simplification in certain flow problems.
9. Which of these is a characteristic of an ideal fluid?
a) It is viscous and compressible
b) It is non-viscous and incompressible
c) It is viscous and incompressible
d) It is non-viscous and compressible
Answer: b) It is non-viscous and incompressible
Explanation: An ideal fluid is a theoretical model with two key properties: zero viscosity (non-viscous) and constant density (incompressible).
10. The dimension of dynamic viscosity is:
a) [M L⁻¹ T⁻¹]
b) [M L T⁻¹]
c) [M L⁻² T⁻²]
d) [M L² T⁻²]
Answer: a) [M L⁻¹ T⁻¹]
Explanation: From the formula for viscosity (τ = µ * du/dy), µ = τ / (du/dy). Shear stress (τ) has dimensions [M L⁻¹ T⁻²] and velocity gradient (du/dy) has [T⁻¹]. So, µ = [M L⁻¹ T⁻²] / [T⁻¹] = [M L⁻¹ T⁻¹].
11. Newton’s law of viscosity states that shear stress is:
a) Inversely proportional to the velocity gradient
b) Directly proportional to the velocity gradient
c) Equal to the square of the velocity gradient
d) Unrelated to the velocity gradient
Answer: b) Directly proportional to the velocity gradient
Explanation: Newton’s law is τ = µ * (du/dy), where shear stress (τ) is directly proportional to the velocity gradient (du/dy), with viscosity (µ) as the constant of proportionality.
12. Fluids which obey Newton’s law of viscosity are called:
a) Ideal fluids
b) Non-Newtonian fluids
c) Newtonian fluids
d) Real fluids
Answer: c) Newtonian fluids
Explanation: Newtonian fluids are those for which the shear stress is linearly proportional to the rate of shear strain (velocity gradient). Water, air, and oil are examples.
13. Which of the following is a Newtonian fluid?
a) Toothpaste
b) Blood
c) Water
d) Paint
Answer: c) Water
Explanation: Water has a constant viscosity regardless of the applied shear stress, making it a Newtonian fluid. The others are non-Newtonian.
14. The velocity gradient in a fluid flow is also known as:
a) Shear strain
b) Shear stress
c) Rate of shear strain
d) Viscous force
Answer: c) Rate of shear strain
Explanation: The derivative du/dy represents the rate at which the layers of fluid are sliding past one another, i.e., the rate of shear strain.
15. The type of fluid flow where viscosity dominates is called:
a) Turbulent flow
b) Compressible flow
c) Laminar flow
d) Supersonic flow
Answer: c) Laminar flow
Explanation: Laminar flow is characterized by smooth, parallel layers of fluid with no disruption between them. Viscous forces are dominant in this regime.
16. The flow between two parallel plates where one is stationary and the other is moving is called:
a) Poiseuille flow
b) Couette flow
c) Plug flow
d) Turbulent flow
Answer: b) Couette flow
Explanation: Couette flow is a type of laminar flow where the fluid motion is induced by the relative movement of two parallel plates.
17. The parabolic velocity profile is characteristic of:
a) Couette flow between moving plates
b) Plug flow in a pipe
c) Poiseuille flow in a pipe
d) Flow of ideal fluid
Answer: c) Poiseuille flow in a pipe
Explanation: For a steady, laminar, fully developed flow of a Newtonian fluid in a pipe, the velocity profile is parabolic due to viscous effects, with maximum velocity at the center.
18. The law governing the rate of flow of a viscous fluid through a capillary tube is:
a) Bernoulli’s theorem
b) Stokes’ law
c) Hagen-Poiseuille law
d) Archimedes’ principle
Answer: c) Hagen-Poiseuille law
Explanation: The Hagen-Poiseuille law describes the volumetric flow rate of a Newtonian fluid in a cylindrical pipe under laminar flow conditions. Q = (πΔP r⁴) / (8µL).
19. According to Hagen-Poiseuille’s law, the flow rate through a capillary tube is proportional to:
a) The radius of the tube
b) The square of the radius
c) The cube of the radius
d) The fourth power of the radius (r⁴)
Answer: d) The fourth power of the radius (r⁴)
Explanation: The flow rate Q ∝ r⁴. This shows that even a small increase in the radius of a blood vessel or pipe drastically increases the flow rate.
20. In a pipe flow, the maximum velocity for laminar flow is how many times the average velocity?
a) 0.5 times
b) 1.0 times
c) 1.5 times
d) 2.0 times
Answer: d) 2.0 times
Explanation: For laminar flow in a circular pipe, the maximum velocity (at the center) is exactly twice the average velocity. U_max = 2 * U_avg.
21. For most liquids, viscosity typically ______ with an increase in temperature.
a) Increases
b) Decreases
c) Remains constant
d) First increases then decreases
Answer: b) Decreases
Explanation: In liquids, increased temperature provides molecules with more thermal energy to break the intermolecular bonds that cause viscosity, making the liquid less viscous (e.g., honey flows easier when warm).
22. For gases, viscosity typically ______ with an increase in temperature.
a) Increases
b) Decreases
c) Remains constant
d) First decreases then increases
Answer: a) Increases
Explanation: In gases, viscosity is caused by molecular momentum transfer. Higher temperature means faster moving molecules, which increases the rate of momentum transfer between layers, thus increasing viscosity.
23. The viscosity of a liquid is primarily due to:
a) Molecular collision
b) Intermolecular cohesion
c) Brownian motion
d) Atomic vibration
Answer: b) Intermolecular cohesion
Explanation: The strong cohesive forces between closely packed molecules in a liquid are the main cause of its viscosity.
24. The viscosity of a gas is primarily due to:
a) Intermolecular cohesion
b) Molecular momentum exchange
c) Gravitational pull
d) Adhesive forces
Answer: b) Molecular momentum exchange
Explanation: Gas molecules are far apart. Viscosity arises when faster-moving molecules from one layer diffuse into a slower-moving layer, transferring momentum and creating an apparent friction.
25. The effect of pressure on the viscosity of liquids is:
a) Negligible
b) Viscosity increases significantly with pressure
c) Viscosity decreases significantly with pressure
d) It follows a sinusoidal pattern
Answer: b) Viscosity increases significantly with pressure
Explanation: For liquids, increasing pressure pushes molecules closer together, strengthening the intermolecular forces and thus increasing viscosity. The effect is more pronounced than in gases.
26. The effect of pressure on the viscosity of gases is:
a) Negligible at moderate pressures
b) Viscosity increases linearly with pressure
c) Viscosity decreases linearly with pressure
d) It follows an exponential pattern
Answer: a) Negligible at moderate pressures
Explanation: For ideal gases, viscosity is independent of pressure. At very high pressures, this changes, but for most practical applications, the effect is negligible.
27. Which formula correctly represents the temperature dependence of gas viscosity?
a) Andrade’s equation
b) Sutherland’s formula
c) Poiseuille’s equation
d) Bernoulli’s equation
Answer: b) Sutherland’s formula
Explanation: Sutherland’s formula provides an expression for estimating the viscosity of a gas as a function of temperature: µ = µ₀ * [(T₀ + C) / (T + C)] * (T/T₀)^(3/2), where C is Sutherland’s constant.
28. The device used to measure the viscosity of a fluid is called a:
a) Barometer
b) Viscometer
c) Hydrometer
d) Manometer
Answer: b) Viscometer
Explanation: A viscometer (or viscosimeter) is an instrument used to measure the viscosity of a fluid.
29. The dimensionless number that predicts the flow regime (laminar or turbulent) is:
a) Mach number
b) Froude number
c) Reynolds number
d) Weber number
Answer: c) Reynolds number
Explanation: The Reynolds number (Re) is the ratio of inertial forces to viscous forces and is the primary parameter for predicting the onset of turbulence.
30. The Reynolds number for flow in a pipe is given by:
a) Re = VD/µ
b) Re = ρVD/µ
c) Re = VD/ν
d) Re = ρVD²/µ
Answer: b) Re = ρVD/µ and c) Re = VD/ν
Explanation: Both are correct as ν = µ/ρ. Therefore, Re = ρVD/µ = VD/ν. D is the characteristic length (diameter for pipe flow).
31. For flow in a pipe, the flow is generally considered laminar if the Reynolds number is:
a) Re < 500
b) Re < 1000
c) Re < 2000
d) Re < 4000
Answer: c) Re < 2000
Explanation: The critical Reynolds number for pipe flow is approximately 2300. For Re < 2000, the flow is always laminar.
32. For flow in a pipe, the flow is generally considered turbulent if the Reynolds number is:
a) Re > 1000
b) Re > 2000
c) Re > 3000
d) Re > 4000
Answer: d) Re > 4000
Explanation: For Re > 4000, the flow is fully turbulent. The range between 2000 and 4000 is the critical transition zone.
33. The Reynolds number is high for:
a) Highly viscous flows
b) Flows where inertial forces dominate
c) Flows where viscous forces dominate
d) Low-density flows
Answer: b) Flows where inertial forces dominate
Explanation: A high Reynolds number (Re = Inertial Forces / Viscous Forces) means inertial forces are much larger than viscous forces, leading to turbulent flow.
34. The Reynolds number is low for:
a) High-velocity flows
b) Flows where viscous forces dominate
c) Flows in large pipes
d) Flows of low-density fluids
Answer: b) Flows where viscous forces dominate
Explanation: A low Reynolds number means viscous forces are dominant over inertial forces, resulting in smooth, laminar flow.
35. The concept of “dynamic similarity” between a model and a prototype is based on the equality of:
a) Reynolds number
b) Froude number
c) Weber number
d) The relevant dimensionless number for the flow
Answer: d) The relevant dimensionless number for the flow
Explanation: For complete dynamic similarity, all relevant dimensionless numbers (Re, Fr, We, Ma, etc.) must be the same. For flow where viscosity is important (e.g., pipe flow, aircraft drag), the Reynolds number must be matched.
36. Stokes’ law gives the expression for:
a) Viscosity of an ideal fluid
b) Drag force on a sphere in a viscous fluid
c) Flow rate through a capillary tube
d) Pressure drop in a pipe
Answer: b) Drag force on a sphere in a viscous fluid
Explanation: Stokes’ law states that the drag force (F) on a small sphere moving through a viscous fluid is given by F = 6πµrv, where µ is viscosity, r is radius, and v is velocity.
37. Stokes’ law is valid for:
a) All Reynolds numbers
b) Very high Reynolds numbers (turbulent flow)
c) Very low Reynolds numbers (creeping flow)
d) Supersonic flow
Answer: c) Very low Reynolds numbers (creeping flow)
Explanation: Stokes’ law is derived for laminar flow conditions where inertia is negligible (Re << 1). It is not accurate for turbulent flow around the sphere.
38. The terminal velocity of a small sphere falling under gravity through a viscous fluid is:
a) Directly proportional to the diameter of the sphere
b) Inversely proportional to the diameter of the sphere
c) Directly proportional to the square of the diameter
d) Inversely proportional to the square of the diameter
Answer: c) Directly proportional to the square of the diameter
Explanation: At terminal velocity, weight = drag + buoyancy. Solving gives v_terminal ∝ (ρ_s – ρ_f) * d² / µ. So, it is proportional to the square of the diameter (d²).
39. When a sphere falls through a fluid, it achieves terminal velocity when:
a) The weight of the sphere equals the viscous drag force
b) The weight of the sphere equals the sum of viscous drag and buoyant force
c) The viscous drag is zero
d) The buoyant force is maximum
Answer: b) The weight of the sphere equals the sum of viscous drag and buoyant force
Explanation: At terminal velocity, the net force is zero. So, downward weight = upward buoyant force + upward viscous drag force.
40. Which factor does NOT affect the terminal velocity of a sphere falling in a fluid?
a) Density of the fluid
b) Density of the sphere
c) Acceleration due to gravity
d) The color of the sphere
Answer: d) The color of the sphere
Explanation: The terminal velocity depends on the physical properties like densities (ρ_s, ρ_f), viscosity (µ), radius (r), and gravity (g). Color is an optical property and has no effect.
41. Fluids that do not obey Newton’s law of viscosity are called:
a) Ideal fluids
b) Real fluids
c) Newtonian fluids
d) Non-Newtonian fluids
Answer: d) Non-Newtonian fluids
Explanation: Non-Newtonian fluids have a viscosity that changes with the applied shear stress or shear rate, so the relationship τ ∝ (du/dy) is not linear.
42. Which of the following is a Non-Newtonian fluid?
a) Water
b) Air
c) Blood
d) Glycerin
Answer: c) Blood
Explanation: Blood’s viscosity decreases with increasing shear rate (shear-thinning behavior), which is a characteristic of non-Newtonian fluids.
43. A fluid whose viscosity decreases with increasing shear rate is called:
a) Dilatant
b) Pseudoplastic
c) Rheopectic
d) Bingham plastic
Answer: b) Pseudoplastic
Explanation: Pseudoplastic fluids are shear-thinning. Their apparent viscosity decreases as the shear rate increases. Examples: ketchup, blood, paint.
44. A fluid whose viscosity increases with increasing shear rate is called:
a) Pseudoplastic
b) Dilatant
c) Thixotropic
d) Ideal
Answer: b) Dilatant
Explanation: Dilatant fluids are shear-thickening. Their apparent viscosity increases as the shear rate increases. Example: a mixture of cornstarch and water.
45. A fluid that behaves as a solid until a minimum yield stress is exceeded is called:
a) Pseudoplastic
b) Dilatant
c) Bingham plastic
d) Rheopectic
Answer: c) Bingham plastic
Explanation: Bingham plastics require a certain yield stress to begin flowing. After that, they can behave like Newtonian fluids. Example: toothpaste, mayonnaise.
46. A fluid whose viscosity decreases over time under a constant shear stress is called:
a) Rheopectic
b) Thixotropic
c) Pseudoplastic
d) Dilatant
Answer: b) Thixotropic
Explanation: Thixotropic fluids have a time-dependent viscosity that decreases under constant shear. Example: some gels and paints (they become thinner when stirred).
47. The opposite of a thixotropic fluid is a:
a) Pseudoplastic fluid
b) Dilatant fluid
c) Rheopectic fluid
d) Bingham plastic
Answer: c) Rheopectic fluid
Explanation: Rheopectic fluids are time-dependent shear-thickening fluids. Their viscosity increases with time under a constant applied shear stress. (Very rare, e.g., some lubricants).
48. The apparent viscosity of a non-Newtonian fluid is:
a) Always constant
b) The ratio of shear stress to shear rate at a given point
c) Equal to the dynamic viscosity
d) Independent of shear rate
Answer: b) The ratio of shear stress to shear rate at a given point
Explanation: For non-Newtonian fluids, the viscosity is not constant. The “apparent viscosity” is defined as the ratio τ / (du/dy) for a specific value of shear rate.
49. The primary function of engine oil in a car is to:
a) Increase power
b) Reduce friction and wear by lubrication
c) Cool the engine
d) Clean the fuel injectors
Answer: b) Reduce friction and wear by lubrication
Explanation: The main job of engine oil (a viscous fluid) is to form a lubricating film between moving metal parts, reducing direct metal-to-metal contact, friction, and wear.
50. Why is viscosity an important property of hydraulic fluids?
a) It determines the color of the fluid
b) It affects the fluid’s ability to transmit power and lubricate
c) It is unrelated to hydraulic system performance
d) It only matters for the cost of the fluid
Answer: b) It affects the fluid’s ability to transmit power and lubricate
Explanation: The viscosity must be high enough to maintain a sealing film for effective power transmission and lubrication but low enough to avoid excessive resistance to flow and power loss.
51. The “viscosity index” (VI) of a lubricant is a measure of:
a) Its density
b) How much its viscosity changes with temperature
c) Its color
d) Its price per liter
Answer: b) How much its viscosity changes with temperature
Explanation: A high viscosity index means the lubricant’s viscosity changes relatively little with temperature, which is a desirable property.
52. Why does honey flow more easily when heated?
a) Its density increases
b) Its viscosity decreases
c) Its surface tension increases
d) It becomes a Newtonian fluid
Answer: b) Its viscosity decreases
Explanation: Heating honey provides thermal energy to break the intermolecular bonds, significantly reducing its viscosity and making it flow more easily.
53. In the human body, the viscosity of blood is primarily influenced by:
a) Body temperature only
b) Hematocrit (red blood cell count) only
c) Both hematocrit and plasma viscosity
d) The heart rate only
Answer: c) Both hematocrit and plasma viscosity
Explanation: Blood viscosity is a key hemodynamic property. It increases with higher hematocrit (percentage of red blood cells) and is also affected by the viscosity of the plasma itself.
54. The phenomenon where the viscosity of a fluid is different at different points in the flow field is a key characteristic of:
a) Ideal flow
b) Compressible flow
c) Non-Newtonian flow
d) Isothermal flow
Answer: c) Non-Newtonian flow
Explanation: For non-Newtonian fluids, the apparent viscosity can vary throughout the flow field depending on the local shear rate, making the analysis more complex.
55. The purpose of a vortex breaker in a tank is to:
a) Increase viscosity
b) Reduce the formation of a vortex during draining
c) Measure the flow rate
d) Heat the fluid
Answer: b) Reduce the formation of a vortex during draining
Explanation: A vortex breaker is a device used to disrupt the circular motion of a fluid (vortex) that can form when draining a tank. This vortex can lead to air entrainment in pumps, which is undesirable. Viscosity influences the formation and strength of these vortices.
56. The boundary layer is a concept introduced by Prandtl to describe:
a) The region where velocity is constant
b) The region where viscous effects are confined near a solid boundary
c) The center of a pipe flow
d) The interface between two immiscible fluids
Answer: b) The region where viscous effects are confined near a solid boundary
Explanation: The boundary layer is the thin layer of fluid immediately adjacent to a solid surface where the velocity changes from zero (no-slip condition) to the free-stream velocity. Viscous effects are significant within this layer.
57. The “no-slip condition” in fluid mechanics states that:
a) A fluid cannot slip past another fluid
b) The velocity of a fluid at a solid boundary is zero relative to the boundary
c) Fluids always slip at boundaries
d) Viscosity is always zero at boundaries
Answer: b) The velocity of a fluid at a solid boundary is zero relative to the boundary
Explanation: This is a fundamental condition for viscous flow. The fluid molecules in contact with the surface adhere to it and have the same velocity as the surface (usually zero if the surface is stationary).
58. The velocity at which the transition from laminar to turbulent flow occurs is called:
a) Sonic velocity
b) Critical velocity
c) Terminal velocity
d) Escape velocity
Answer: b) Critical velocity
Explanation: The critical velocity is the velocity at which the flow transitions from laminar to turbulent. It corresponds to the critical Reynolds number.
59. The loss of pressure in a pipe flow is primarily due to:
a) Change in elevation
b) Viscosity of the fluid
c) Change in density
d) Change in temperature
Answer: b) Viscosity of the fluid
Explanation: Frictional losses due to fluid viscosity are the primary cause of pressure drop in a pipe for a given flow rate. This is described by the Darcy-Weisbach equation.
60. The Moody chart is used to find:
a) Viscosity of a fluid
b) The friction factor for pipe flow
c) The velocity profile
d) The Reynolds number for given flow
Answer: b) The friction factor for pipe flow
Explanation: The Moody chart plots the Darcy friction factor (f) as a function of Reynolds number (Re) and relative roughness (ε/D) for pipe flow. It is used to calculate frictional head loss.
61. Kinematic viscosity is more useful than dynamic viscosity when analyzing flows involving:
a) Significant pressure changes
b) Significant gravitational forces and inertia
c) Only compressible fluids
d) Only non-Newtonian fluids
Answer: b) Significant gravitational forces and inertia
Explanation: Kinematic viscosity (ν) appears in the Reynolds number (Re = VD/ν), which compares inertial to viscous forces. It is therefore central to problems where both gravity/inertia and viscosity are important (e.g., modeling waves, flow in channels).
62. The drag force on an object moving through a fluid at very low Reynolds numbers is primarily due to:
a) Pressure drag
b) Skin friction drag
c) Wave drag
d) Induced drag
Answer: b) Skin friction drag
Explanation: At very low Re (creeping flow), viscous forces dominate. The drag is almost entirely due to skin friction (viscous shear stress), not due to pressure differences (form drag).
63. The drag force on an object moving through a fluid at very high Reynolds numbers is primarily due to:
a) Skin friction drag
b) Pressure drag (form drag)
c) Both are equally important
d) Neither is important
Answer: b) Pressure drag (form drag)
Explanation: At high Re, inertial forces dominate. Flow separation occurs, creating a wake and a large pressure difference between the front and back of the object, leading to dominant pressure drag.
64. The coefficient of viscosity (µ) for an ideal fluid is:
a) Zero
b) Unity
c) Infinity
d) Constant but non-zero
Answer: a) Zero
Explanation: By definition, an ideal fluid is inviscid (has no viscosity), so its coefficient of viscosity, µ, is zero.
65. The viscous force (F) on a plate moving over a fluid film is proportional to its velocity (V) as:
a) F ∝ V
b) F ∝ V²
c) F ∝ 1/V
d) F ∝ √V
Answer: a) F ∝ V
Explanation: From Newton’s law of viscosity, the shear stress τ = µ (du/dy) is linear with velocity. Therefore, the integrated force F = τ * Area will also be directly proportional to the plate velocity V.
66. The falling sphere viscometer works on the principle of:
a) Bernoulli’s theorem
b) Stokes’ law
c) Hagen-Poiseuille law
d) Pascal’s law
Answer: b) Stokes’ law
67. In a capillary tube viscometer, the viscosity is proportional to:
a) Time of flow
b) (Time of flow)²
c) 1 / (Time of flow)
d) √(Time of flow)
Answer: a) Time of flow
68. The Saybolt Universal Viscometer measures viscosity in terms of:
a) Poise
b) Seconds
c) Stokes
d) Pascal-second
Answer: b) Seconds
69. The property of a fluid which enables it to resist tensile stress is known as:
a) Viscosity
b) Surface tension
c) Compressibility
d) Capillarity
Answer: b) Surface tension (Often confused with viscosity)
70. The ratio of the viscosity of a solution to the viscosity of the solvent is called:
a) Relative viscosity
b) Specific viscosity
c) Reduced viscosity
d) Inherent viscosity
Answer: a) Relative viscosity
71. The viscosity of an ideal gas _______ with density.
a) Increases
b) Decreases
c) Is independent
d) Is inversely proportional
Answer: c) Is independent (At moderate pressures)
72. The viscosity of a liquid _______ with density.
a) Increases
b) Decreases
c) Is independent
d) Is inversely proportional
Answer: a) Increases (Generally, denser liquids have stronger intermolecular forces)
73. The eddy viscosity is a concept used in the analysis of:
a) Laminar flow
b) Turbulent flow
c) Creeping flow
d) Compressible flow
Answer: b) Turbulent flow
74. The dynamic viscosity of water at 20°C is approximately:
a) 0.01 Poise
b) 1 Poise
c) 0.1 Poise
d) 10 Poise
Answer: a) 0.01 Poise (1 cP = 0.01 P. Water’s viscosity is ~1 cP)
75. The dynamic viscosity of air at 20°C is approximately:
a) 0.0001 Poise
b) 0.01 Poise
c) 0.1 Poise
d) 1 Poise
Answer: b) 0.01 Poise (Air’s viscosity is ~0.018 cP, which is ~0.00018 P. Closest is 0.01 P from the options, but it’s a trick question. The correct order is air << water. 0.01 P is 1 cP, which is water. Air is 0.00018 P. Among options, (a) is best.)
Correction for 75: The best answer is a) 0.0001 Poise, as it is closest to the actual value of 0.00018 Poise.
76. The viscous sublayer is a region in:
a) Laminar flow away from walls
b) The turbulent boundary layer very close to the wall
c) The core of a turbulent flow
d) A free jet
Answer: b) The turbulent boundary layer very close to the wall
77. The viscosity of a mixture of two miscible liquids is often:
a) The average of their viscosities
b) Less than the viscosity of either component
c) More than the viscosity of either component
d) Unpredictable without experiment
Answer: d) Unpredictable without experiment (It can be higher or lower)
78. The “apparent viscosity” of a Bingham plastic fluid after yielding is:
a) Zero
b) Constant
c) Increasing with shear rate
d) Decreasing with shear rate
Answer: b) Constant (It often behaves like a Newtonian fluid post-yield)
79. The Weissenberg effect is exhibited by:
a) Newtonian fluids
b) Viscoelastic fluids
c) Ideal fluids
d) Dilatant fluids
Answer: b) Viscoelastic fluids (e.g., the fluid climbs up a rotating rod)
80. The viscosity of a fluid is a _______ property.
a) Thermodynamic
b) Kinematic
c) Transport
d) Chemical
Answer: c) Transport (It transports momentum)
81. The Navier-Stokes equations are a statement of:
a) Newton’s first law for an ideal fluid
b) Newton’s second law for a viscous fluid
c) The conservation of energy
d) The conservation of mass
Answer: b) Newton’s second law for a viscous fluid
82. The term µ∇²V in the Navier-Stokes equation represents:
a) Inertial force
b) Pressure force
c) Gravity force
d) Viscous force
Answer: d) Viscous force
83. For a given fluid, if the kinematic viscosity is 0.01 Stoke and the density is 0.1 g/cm³, the dynamic viscosity is:
a) 0.001 Poise
b) 0.01 Poise
c) 0.1 Poise
d) 1 Poise
Answer: a) 0.001 Poise (µ = ν * ρ = 0.01 cm²/s * 0.1 g/cm³ = 0.001 g/(cm·s) = 0.001 P)
84. The velocity profile for a power-law fluid in a pipe is:
a) Always parabolic
b) parabolic only if n=1
c) Always linear
d) Independent of ‘n’
Answer: b) parabolic only if n=1 (n=1 is the Newtonian case)
85. The power-law model for non-Newtonian fluids is given by τ = K(du/dy)ⁿ. For a pseudoplastic fluid, ‘n’ is:
a) n < 1
b) n = 1
c) n > 1
d) n = 0
Answer: a) n < 1
86. The property of “thixotropy” is crucial in the application of:
a) Structural paints
b) Lubricating oils
c) Hydraulic fluids
d) Jet fuel
Answer: a) Structural paints (They should be thick on the can but thin when brushed)
87. The viscosity of a gas is _______ of pressure at moderate conditions.
a) Dependent
b) Independent
c) Inversely proportional
d) Proportional to the square root
Answer: b) Independent
88. The viscosity of a liquid is _______ of pressure.
a) Largely independent
b) Highly dependent
c) Inversely proportional
d) Unrelated
Answer: b) Highly dependent
89. The term “absolute viscosity” is another name for:
a) Kinematic viscosity
b) Dynamic viscosity
c) Apparent viscosity
d) Relative viscosity
Answer: b) Dynamic viscosity
90. The viscosity of an ideal fluid, as per definition, is:
a) Zero
b) Infinite
c) Same as water
d) Same as air
Answer: a) Zero
91. The friction factor for laminar flow in a pipe (Re<2000) is given by:
a) f = 16/Re
b) f = 64/Re
c) f = 0.0791/Re^(1/4)
d) f is constant
Answer: b) f = 64/Re
92. The friction factor for smooth turbulent pipe flow is given approximately by:
a) f = 64/Re
b) f = 0.316/Re^(1/4) (Blasius formula)
c) f = constant
d) f = 16/Re
Answer: b) f = 0.316/Re^(1/4)
93. The viscosity of a fluid plays a dominant role in determining the _______ of a body moving through it.
a) Lift
b) Drag
c) Both lift and drag
d) Neither
Answer: c) Both lift and drag (Via skin friction and influencing flow separation)
94. The viscosity of magma primarily determines the:
a) Color of a volcano’s smoke
b) Explosivity of a volcanic eruption
c) Height of a volcano
d) Temperature of lava
Answer: b) Explosivity of a volcanic eruption (High viscosity magma traps gas, leading to explosive eruptions)
95. In the context of lubrication, a high viscosity index (VI) is desirable because it means the lubricant:
a) Is very thick
b) Is very cheap
c) ‘s viscosity changes less with temperature
d) ‘s viscosity changes more with temperature
Answer: c) ‘s viscosity changes less with temperature
96. The “viscous damping” in mechanical systems uses the principle of viscosity to:
a) Amplify vibrations
b) Dissipate energy and suppress vibrations
c) Increase speed
d) Reduce friction
Answer: b) Dissipate energy and suppress vibrations
97. The flow of a viscous fluid between two concentric rotating cylinders is used to measure viscosity in a:
a) Capillary viscometer
b) Falling sphere viscometer
c) Rotational viscometer
d) Saybolt viscometer
Answer: c) Rotational viscometer (e.g., Couette viscometer)
98. The velocity gradient (du/dy) is maximum at the wall for:
a) Plug flow
b) Laminar flow in a pipe
c) Turbulent flow in a pipe
d) Ideal flow
Answer: b) Laminar flow in a pipe (The shear stress and velocity gradient are maximum at the wall)
99. The viscosity of a fluid is a measure of its internal resistance to:
a) Flow
b) Compression
c) Heat transfer
d) Sound transmission
Answer: a) Flow
100. For a Newtonian fluid, the plot between shear stress (τ) and shear rate (du/dy) is:
a) A straight line through the origin
b) A curve that starts at a yield stress
c) A curve that bends upwards
d) A curve that bends downwards
Answer: a) A straight line through the origin