A tuning fork of frequency 340 Hz is vibrated just above the tube of 120 cm height. Water is poured slowly in the tube. What is the minimum height of water necessary for the resonance? (speed of sound in the air = 340m/s)

Options

A. 15 cm
B. 25 cm
C. 30 cm
D. 45 cm

Answer

D

Explanation

`f_("closed")=((2n-1)v)/(4l)`
`implies 340=((2n-1)xx340)/(4xxl)=1=((2n-1))/(4xxl)m`
`implies l=((2n-1)/(4))xx100cm`
`n=1,l=25cm`
`n=2,l=75cm`
`n=3,l=125cm`
only 25 cm, 75 cm are possible
Corresponding length of water column
`=120-25=95cm`
and `(120-75)=45cm`.