A tuning fork of frequency n is sounded at the open end of a long cylindrical tube having a side opening…

Q: A tuning fork of frequency n is sounded at the open end of a long cylindrical tube having a side opening and fitted with a movable reflecting piston, On moving the piston through 9 cm, the intensity of sound heard by the listener changes from max. to minimum. If speed of sound is 360 m/s, value of n is

(a) 1000 Hz

(b) 250 Hz

(c) 500 Hz

(d) 750 Hz

Ans:(a)

Sol: For change on intensity from maximum to minimum, path diff. = λ/2

λ/2 = (9 + 9)cm,

λ = 36 cm

n = v/λ

= (360×100)/360

= 1000 Hz