Q.85 A current meter is a device used for measuring the:
- Apressure of the fluid
- Bsurface tension of the fluid
- Cviscosity of the fluid
- Dvelocity of the flow of the fluidCorrect
Solution
Concept
A current meter measures the velocity of flowing water in rivers, streams and canals.
Formula
v = a Ns + b
Step-by-step solution
1. A current meter has a rotating element (cups or propeller). 2. The flowing water turns the rotor. 3. The number of revolutions per second (Ns) is counted. 4. The calibration equation v = a Ns + b gives the flow velocity. 5. So a current meter measures the velocity of flow. Answer is D.
Explanation
A current meter is put in flowing water, and its rotor turns with the flow. The speed of rotation is related to water velocity by a calibration equation. It is widely used to measure stream velocity and then discharge.
Why the other options are wrong
A: Pressure is measured by a piezometer, manometer or pressure gauge. B: Surface tension is measured by a tensiometer or the capillary rise method. C: Viscosity is measured by a viscometer.
Shortcut
Current meter = current (flow) speed = velocity.
Common mistake
Confusing a current meter with an electrical ammeter, or thinking it measures discharge directly.
Correct answer: D) velocity of the flow of the fluid