Surface Tension, Capillarity and Excess Pressure

Surface Tension, Capillarity and Excess Pressure

A spray tube (10cm2) has 50 holes of diameter 0.9mm. If the flow speed is 2.5m/min, what is the ejection speed?

A1v1 = A2v2, v1 = 2.5m/min = 0.04167m/s, A1 = 10×10−4m2. Hole area: Ah = π(0.45×10−3)2, total A2 = 50×π×2.025×10−7≈3.181×10−5m2. v2 = 10×10−4×0.041673.181×10−5≈1.31m/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 1.3 m/s. 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

A container has whole blood (ρ\=1.06×103kg/m3) up to 1.5m. What is the gauge pressure at the bottom? (Take g\=9.8m/s2)

Gauge pressure: Pg = ρgh. ρ = 1.06×103kg/m3, g = 9.8m/s2, h = 1.5m. Pg = 1.06×103×9.8×1.5 = 15582Pa. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 1.56 × 10⁴ Pa. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCBI Bookshelf, Ideal Gas Law: P1V1/T1 = P2V2/T2.

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Surface Tension, Capillarity and Excess Pressure

Which of the following statements is correct about atmospheric pressure?

Atmospheric pressure decreases with altitude as the weight of the air column above reduces, a fundamental concept in the chapter’s discussion of pressure variation. As per NCERT, applying relevant law/formula with correct units and sign convention leads to It decreases with altitude. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCBI Bookshelf, Ideal Gas Law: P1V1/T1 = P2V2/T2.

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Surface Tension, Capillarity and Excess Pressure

Why does the pressure in a fluid decrease when its speed increases in a horizontal pipe?

Bernoulli’s principle states that in steady flow, an increase in kinetic energy (12ρv2) corresponds to a decrease in pressure energy, as total energy is conserved along a horizontal streamline. As per NCERT, applying relevant law/formula with correct units and sign convention leads to Because of energy conservation. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCBI Bookshelf, Ideal Gas Law: P1V1/T1 = P2V2/T2.

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Surface Tension, Capillarity and Excess Pressure

A hydraulic press uses a small piston of area 0.008m2 to exert 120N. What force is produced by a large piston of area 0.

Pascal’s law: P = F1A1 = F2A2. F2 = F1×A2A1. F1 = 120N, A1 = 0.008m2, A2 = 0.032m2. F2 = 120×0.0320.008 = 120×4 = 480N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 480 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 spray tube (7cm2) has 35 holes of diameter 0.8mm. If the flow speed is 3.0m/min, what is the ejection speed?

A1v1 = A2v2, v1 = 3.0m/min = 0.05m/s, A1 = 7×10−4m2. Hole area: Ah = π(0.4×10−3)2, total A2 = 35×π×1.6×10−7≈1.759×10−5m2. v2 = 7×10−4×0.051.759×10−5≈1.99m/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 2.0 m/s. 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

Which statement is incorrect about dynamic lift?

Dynamic lift (e.g., on airplane wings) results from a pressure difference due to faster airflow above (Bernoulli’s principle), not viscosity or gravitational force alone. The incorrect statement is that it’s due to viscosity.

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

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Surface Tension, Capillarity and Excess Pressure

A bubble of radius 4mm is formed at 50cm depth in a soap solution (ρ\=1.2×103kg/m3, S\=0.025N/m). What is the total pres

Pi = Pa+ρgh+2Sr. Pa = 1.01×105Pa, ρgh = 1.2×103×9.8×0.5 = 5880Pa. 2Sr = 2×0.0254×10−3 = 12.5Pa. Pi = 1.01×105+5880+12.5 = 1.06892×105Pa. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 1.069 × 10⁵ Pa. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCBI Bookshelf, Ideal Gas Law: P1V1/T1 = P2V2/T2.

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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

What is the force on a submarine window (0.06m2) at 400m depth in seawater (ρ\=1.03×103kg/m3), interior at atmospheric p

Gauge pressure: Pg = ρgh = 1.03×103×9.8×400 = 4.0376×106Pa. F = PgA = 4.0376×106×0.06 = 2.42256×105N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 2.4 × 10⁵ N. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCBI Bookshelf, Ideal Gas Law: P1V1/T1 = P2V2/T2.

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Surface Tension, Capillarity and Excess Pressure

What is the primary reason a sharp needle pierces the skin more easily than a blunt object with the same force?

Pressure is defined as force per unit area (P = F/A). A sharp needle has a smaller contact area, resulting in higher pressure for the same force, making it easier to penetrate the skin compared to a blunt object with a larger area.

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

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Surface Tension, Capillarity and Excess Pressure

A 1500kg car is lifted by a hydraulic system with a small piston of radius 6cm and a large piston of radius 18cm. What f

F1 = A1A2F2, F2 = 1500×9.8 = 14700N. A1 = π(0.06)2, A2 = π(0.18)2, A1A2 = 0.00360.0324 = 19. F1 = 147009 = 1633.33N≈1633N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 1633 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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