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. `25 cm`
B. `95 cm`
C. `75 cm`
D. `45 cm`

Answer

D

Explanation

`lambda = (nu) / (f) = (340) / (340) = 1 m = 100 cm`
`(lambda) / (4) = 25 cm`
Air column length required are,
`(lambda) / (4)` , `(3 lambda) / (4)` , `(5 lambda) / (4)` etc.
or `25 cm` , `125 cm` etc.
maximum we can take `75 cm`.
:. minimum water length
= `120 - 75 = 45 cm`