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JEE Main & Advanced Physics Wave Mechanics Question Bank Critical Thinking

  • question_answer
    Vibrating tuning fork of frequency n is placed near the open end of a long cylindrical tube. The tube has a side opening and is fitted with a movable reflecting piston. As the piston is moved through 8.75 cm, the intensity of sound changes from a maximum to minimum. If the speed of sound is 350 m/s. Then n is

    A)            500 Hz                                     

    B)            1000 Hz

    C)            2000 Hz                                   

    D)            4000 Hz

    Correct Answer: B

    Solution :

               When the piston is moved through a distance of 8.75cm, the path difference produced is \[2\times 8.75\,cm=17.5\,cm\]. This must be equal to\[\frac{\lambda }{2}\] for maximum to change to minimum.  \ \[\frac{\lambda }{2}=17.5\]cm Þ \[\lambda =35cm=0.35m\] So, \[v=n\lambda \]Þ \[n=\frac{v}{\lambda }=\frac{350}{0.35}=1000Hz\]


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