Question

A glass tube of length `1.0` m is completely filled with
water. A vibrating tuning fork of frequency `500` Hz is
kept over the mouth of the tube and the water is
drained out slowly at the bottom of the tube. If the
velocity of sound in air is 330 `ms^(-1)`, then the total
number of resonances that occur will be
A. 2
B. 3
C. 1
D. 5

Answer 1

Correct Answer - a
Frequency, `v=v/(4l) or l=v/(4v)`
`therefore l_(1) = v/(4v_(1))=330/(4xx500)=0.165m,`
`l_(2)=(3v)/(4v_(1))=3l_(1)=0.495`
`l_(3)=(5v)/(4v_(1))=5l_(1)=0.825m`
and `l_(4)=(7v)/(4v_(1))=7l_(1)=1.155 gt 1 m`
Therefore, number of resonance = 3