A tuning fork of frequency `340 Hz` is excited and held above a cylindrical tube of length `120 cm`. It is slowly filled with water. The minimum height of water column required for resonance to be first heard( Velocity of sound `=340 ms^-1`) is.

Options

A. 5 cm
B. 25 cm
C. 45 cm
D. 120 cm

Answer

A

Explanation

As the tuning fork is in resonance with air column in the pipe closed at one end
`f = (nv)/(4l)` with `n =1 , 3 , 5`
So length of air column in the pipe
`h = (nv)/(4f) 25 n cm`
i.e. `L = 25 cm , 75 cm , 125 cm`
So `L = h = 130 cm`
`h = 130 - L`
`h_(min)=130-L_(max) = 130-125 =5cm`