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.
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.
Textbook Speed Formula
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.
