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#viscosity

13 public questions tagged with this topic.

Surface Tension, Capillarity and Excess Pressure

Why does the viscosity of liquids generally decrease with increasing temperature?

Higher temperatures increase molecular kinetic energy in liquids, weakening intermolecular forces, reducing resistance to flow, and thus lowering viscosity, as noted in the chapter. As per NCERT, applying relevant law/formula with correct units and sign convention leads to Intermolecular forces weaken. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Surface Tension, Capillarity and Excess Pressure

Why does a fluid’s viscosity contribute to energy loss in real flow systems?

Viscosity causes internal friction between fluid layers, converting kinetic energy into heat through shear stress, leading to energy dissipation, which Bernoulli’s ideal flow neglects. As per NCERT, applying relevant law/formula with correct units and sign convention leads to It converts kinetic energy to heat. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Equation of Continuity and Flow Rate

A sphere of radius 0.04m moves at 0.12m/s through honey (η\=0.2Pa s). What is the viscous drag force?

Stokes’ law: F = 6πηav. η = 0.2Pa s, a = 0.04m, v = 0.12m/s. F = 6×3.14×0.2×0.04×0.12 = 0.1809N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 0.18 N. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Equation of Continuity and Flow Rate

A plate of area 0.08m2 moves at 0.8m/s over a 0.7mm thick glycerine film (η\=0.83Pa s). What force is required?

Viscous force: F = ηvAl. η = 0.83Pa s, v = 0.8m/s, A = 0.08m2, l = 0.7×10−3m. F = 0.83×0.8×0.080.7×10−3 = 0.83×91.43 = 75.89N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 76 N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Equation of Continuity and Flow Rate

A plate of area 0.05m2 moves at 0.7m/s over a 0.8mm thick water film (η\=1.0×10−3Pa s). What force is required?

Viscous force: F = ηvAl. η = 1.0×10−3Pa s, v = 0.7m/s, A = 0.05m2, l = 0.8×10−3m. F = 1.0×10−3×0.7×0.050.8×10−3 = 1.0×10−3×43.75 = 0.04375N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 0.044 N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Fluid Pressure, Pascal's Law and Manometers

Which of the following statements is correct about viscosity?

Viscosity measures a fluid’s resistance to flow due to internal friction between layers, decreasing with temperature in liquids as cohesive forces weaken, not increasing. As per NCERT, applying relevant law/formula with correct units and sign convention leads to It measures resistance to flow. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Fluid Pressure, Pascal's Law and Manometers

A plate of area 0.07m2 moves at 0.6m/s over a 0.9mm thick machine oil film (η\=0.113Pa s). What force is required?

Viscous force: F = ηvAl. η = 0.113Pa s, v = 0.6m/s, A = 0.07m2, l = 0.9×10−3m. F = 0.113×0.6×0.070.9×10−3 = 0.113×46.67 = 5.27N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 5.3 N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Surface Tension, Capillarity and Excess Pressure

A plate of area 0.09m2 moves at 0.5m/s over a 1.0mm thick water film (η\=1.0×10−3Pa s). What force is required?

Viscous force: F = ηvAl. η = 1.0×10−3Pa s, v = 0.5m/s, A = 0.09m2, l = 1.0×10−3m. F = 1.0×10−3×0.5×0.091.0×10−3 = 1.0×10−3×45 = 0.045N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 0.045 N. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Viscosity, Stokes' Law and Reynolds Number

A plate of area 0.08m2 moves at 0.4m/s over a 0.25mm thick oil film (η\=0.034Pa s). What force is required?

Viscous force: F = ηvAl. η = 0.034Pa s, v = 0.4m/s, A = 0.08m2, l = 0.25×10−3m. F = 0.034×0.4×0.080.25×10−3 = 0.034×128 = 4.352N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 4.35 N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Fluid Pressure, Pascal's Law and Manometers

A plate of area 0.06m2 moves at 0.6m/s over a 0.4mm thick glycerine film (η\=0.83Pa s). What force is required?

Viscous force: F = ηvAl. η = 0.83Pa s, v = 0.6m/s, A = 0.06m2, l = 0.4×10−3m. F = 0.83×0.6×0.060.4×10−3 = 0.83×90 = 74.7N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 74.7 N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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