Page 153 - Physics - XI

Principle/Theory

The venturimeter is a gauge used to measure the fl ow rate of a fl uid when the motion of fl uid is steady.
Its working is based on Bernoulli's theorem. For horizontal fl ow,

1
P V = Constant …(1)
2
2
As per the equation of continuity,

aV = constant …(2)
P = ρgh …(3)
where, P is the static pressure.

ρ is the density of fl uid (water).

V is the velocity of fl uid.
a is the area of cross-section of pipe.

There is a low pressure in a region where velocity of fl uid is high and vice-versa. The velocity of fl uid is
high at the narrow cross-section and vice-versa.

Procedure
1. Measure the internal diameters of both the horizontal pipes A and B by using Vernier Calliper at least
two times to determine the area of cross-section of pipes.

2. Join the pipes A and B in such a way that there must not be any leakage of water at the junction.
3. Place two pipes A and B horizontally on the table so that the tubes C and D remain vertical and parallel

to each other.
4. Open the water tap at a slow rate so that fl ow of water remains steady in the pipes A and B.
5. Measure the heights of water in the tubes C and D by the metre scale to calculate the pressure.

6. Increase the rate of tap water in the pipes A and B for two more reading and repeat step 5.

Observations

1. Least count of Vernier Calliper = _________ cm

2. Zero error of Vernier Calliper = z = _________ cm

3. Internal diameter of pipe A, d = _________ cm
A
4. Corrected diameter of pipe A, d = d + z = _________ cm
1 A
5. Internal diameter of pipe B, d = _________ cm
B
6. Corrected diameter of pipe B, d = d + z = _________ cm
2 B
As aV = constant

So, the pipe having smaller area of cross-section will have higher fl ow rate.

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