Topic 6.6.46 min read
Venturi Meter
A Venturi meter measures fluid flow using a wide section, a narrow throat and the pressure difference created by their different speeds.
Choose Your Level
Beginner Level
A Venturi meter narrows a pipe. Fluid speeds up in the throat, pressure falls, and the measured pressure difference reveals the flow speed.
Recommended for Class 11
Venturi Meter
Overview
A Venturi meter measures fluid flow using a wide section, a narrow throat and the pressure difference created by their different speeds.
Learning Outcomes
- Continuity makes fluid faster in the narrow throat.
- Bernoulli gives lower throat pressure.
- Manometer height h measures pressure difference.
- The textbook result gives inlet speed from A₁, A₂ and h.
Intermediate Level
Construction and Working
Section 1 has area A₁, speed v₁ and pressure P₁. The throat has smaller area A₂, greater speed v₂ and lower pressure P₂.
Pressure Difference
Textbook Speed Formula
Simple Venturi Ratio
A throat area is half the inlet area and inlet speed is 3.0 m s⁻¹. Find throat speed.
A₁v₁ = A₂v₂
v₂ = (A₁A₂)v₁
v₂ = 2 × 3.0
Final answer: v₂ = 6.0 m s⁻¹
Carburettor Connection
Fast air at a Venturi throat lowers pressure, allowing higher atmospheric pressure to push petrol into the air stream.
Common Mistakes
- Do not reverse the high-speed and low-pressure regions.
- State the ideal-flow conditions before using Bernoulli reasoning.
- Use consistent SI units in calculations.
Short-Question Preparation
Q. What does a Venturi meter measure?
A. The flow speed or volume flow rate of fluid in a tube.
Q. Why is pressure lower at the throat?
A. The smaller area produces greater speed, so Bernoulli pressure is lower.
Q. How is flow rate found?
A. After finding speed, use Q = Av.
Sticky Notes
- Continuity makes fluid faster in the narrow throat.
- Bernoulli gives lower throat pressure.
- Manometer height h measures pressure difference.
- The textbook result gives inlet speed from A₁, A₂ and h.
60-Second Revision
A Venturi meter measures fluid flow using a wide section, a narrow throat and the pressure difference created by their different speeds.
Ask-the-Tutor Modes
- Explain it simply.
- Show the physics step by step.
- Solve a numerical example.
- Prepare me for an exam question.
- Test me with an MCQ.
Exam Focus
Exam Focus
Important points
- Continuity makes fluid faster in the narrow throat.
- Bernoulli gives lower throat pressure.
- Manometer height h measures pressure difference.
- The textbook result gives inlet speed from A₁, A₂ and h.
Common exam traps
- Reversing pressure and speed
Long question structure
Definition → mechanism → equations → application.
Common Mistakes
Common Mistakes
- Mistake
Check speed, pressure and height carefully.
Revision Zone
60-Second Revision
Quick cues from this topic — use them for last-minute revision.
Continuity makes fluid faster in the narrow throat.
Bernoulli gives lower throat pressure.
Manometer height h measures pressure difference.
The textbook result gives inlet speed from A₁, A₂ and h.
A Venturi meter measures fluid flow using a wide section, a narrow throat and the pressure difference created by their different speeds.
- Definition
- A Venturi meter measures fluid flow using a wide section, a narrow throat and the pressure difference created by their different speeds.
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Exam Practice
Important Question
Q1. What does a Venturi meter measure?
Important Question
Q2. Why is pressure lower at the throat?
Important Question
Q3. How is flow rate found?