Q.17 Physics ⭐ 360° Option Elimination Active
NEET 2023 Physics Question 17 Solution
Topic: Mechanical Properties of Fluids · Official NTA Booklet Code G5
Question
The venturi-meter works on:
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Verified Against NTA Final Answer Key
Option (3) : Bernoulli's principle
📚 Mechanical Properties of Fluids Easy
📋 Given Parameters & Problem Setup
Device Venturi-meter
Target Governing physical principle
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⏱️ Save ~30 seconds The 30-Second Exam Hall Shortcut: ⚡ Direct Instrument Principle Association
A Venturi-meter measures flow speed using constriction pressure difference (P₁ - P₂ = 1/2 ρ (v₂² - v₁²)), which is a direct application of Bernoulli's Principle!
1 Recall what a Venturi-meter does: measures the rate of flow of an incompressible fluid through a constricted pipe.
2 At the throat (narrow cross-section), velocity increases (A₁v₁ = A₂v₂), so by conservation of energy, pressure drops.
3 The pressure head difference h governs flow velocity via Bernoulli's equation: P + (1/2)ρv² + ρgh = constant.
4 Pick Option (3) Bernoulli's principle in 2 seconds!
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Why You Can 100% Trust This Shortcut: NCERT Physics · Mechanical Properties of Fluids (Fluid dynamics devices: Venturi-meter is based on Bernoulli's principle).
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Step-by-Step Rigorous Workflow & Mathematical Proof
Step 1
Function and Geometry of a Venturi-meter
A Venturi-meter is a device used for measuring the speed of flow of an incompressible fluid in a pipe. It consists of a broad entrance tube of area A₁, a constricted throat of area A₂, and a manometer to record the pressure difference between the two sections.
Step 2
Application of Continuity and Bernoulli's Equations
By the equation of continuity, as area decreases at the throat (A₂ < A₁), the fluid velocity increases (v₂ > v₁):
Step 3
Bernoulli's Pressure Drop Formulation
For horizontal streamline flow, Bernoulli's principle states that the total mechanical energy per unit volume is constant:
Step 4
Conclusion
Thus, the functioning of a Venturi-meter is fundamentally based on Bernoulli's principle.
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4-Option Deep Scan
360° Option Elimination Engine Key Feature
Diagnose every choice: Know exactly why the right option works and why distractors fail.
1 (1)
✗ Incorrect Verdict & Scientific Reason:
Applies to moments of inertia of planar rigid bodies, unrelated to fluids.
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Student Fallacy (Why candidates pick this trap): Candidate picked an unrelated mechanics theorem.
2 (2)
✗ Incorrect Verdict & Scientific Reason:
Governs wave optics and wavefront propagation.
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Student Fallacy (Why candidates pick this trap): Candidate confused optics principles with hydrodynamics.
3 (3)
✓ 100% Correct Verdict & Scientific Reason:
Verbatim canonical textbook truth: Venturi-meter functions on Bernoulli's theorem.
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Why this is airtight: None. Candidate recognized standard fluid flow apparatus.
4 (4)
✗ Incorrect Verdict & Scientific Reason:
Applies to moment of inertia about parallel axes (I = I_cm + Md²).
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Student Fallacy (Why candidates pick this trap): Candidate picked an unrelated rigid body mechanics theorem.
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NTA Trap Alert: Distractor Options from Unrelated Domains
NTA provided two rotational mechanics options (parallel and perpendicular axes) and one optics option (Huygens) alongside Bernoulli's principle.
🛡️ How to avoid the -1 mark: Associate standard devices: Venturi-meter, Atomizer/Sprayer, Dynamic lift on wings = Bernoulli's Principle.
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Core NEET Syllabus Standard
National Eligibility cum Entrance Test (NEET UG) · Mechanical Properties of Fluids Standard Benchmark
Core Scientific Principle Tested:
"In horizontal fluid flow, higher velocity corresponds to lower static pressure: P + 1/2 ρv² = constant."
Syllabus Focus: Bernoulli's Principle and Its Applications
Preserved in Rationalized Curriculum Syllabus & Academic Standards ↗
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