Why correction of 0.57 off the radius of tube must be added in measuring the shortest length of air column?

Question

Sound Resonance

1. Measure the distance from he open end of the tube to the water level. Record this as the first resonance length(L1)

2. Determine the second resonance by allowing the level of water to go down further until the loudest sound is produced.

3. Measure the distance from the open end of the tube to the water level. Record this as the second resonance length(L2)

4. Carefully measure the inner diameter of the tube by using a vernier caliper and record it. From the inner diameter, determine the inner radius and then take 57% of the inner radius as correction "c" factor which is to be addedto the measured resonance lengths

5. Compute the speed of sound in air from the equations:

First resonance: V1=4f(L1+C)
Second resonance: V2=(4f(L2+c))/3

Answer 1

This is called end effect.
The distortion of the standing wave take the form of almost a hemisphere added to the end of the tube ie50% of the diameter.