• # question_answer A long cylindrical tube carries a highly polished piston and has a side opening. A tunning fork of frequency v is sounded at the sound heard by the listener changes if the piston is moved in or out. At a particular position of the piston is moved through a distance of 9 cm, the intensity of sound becomes minimum, if the speed of sound is 360 m/s, the value of v is: A)  129.6 Hz                      B)  500 Hz C)  1000 Hz                       D) 2000 Hz

Correct Answer: C

Solution :

When piston moves a distance x^, path difference change by 2x. $\therefore$ The path difference between maxima and consecutive minima = $\lambda /2$ $2x=\lambda /2$ or $\lambda =4xf\,=4\times 9\,\,cm\,=36\,cm\,=0.36\,cm$ $v=\frac{v}{\lambda }=\frac{360}{0.36}\,=1000\,Hz$

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