A Venturi meter measures the rate of flow of a fluid by using

  • A. the temperature rise in a constriction
  • B. the pressure difference between a wide section and a narrow section
  • C. the weight of the fluid
  • D. the colour change of the fluid

Explanation

The fluid speeds up in the throat, so its pressure falls, and measuring that pressure drop with a manometer gives the speed through the continuity and Bernoulli equations. Because it has no moving parts it is reliable and causes little permanent pressure loss. The same principle drives a carburettor and a filter pump.

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