NEET Sample Paper NEET Sample Test Paper-41

  • question_answer
    A closed pipe and an open pipe of same length produce 2 beats, when they are set into vibration simultaneously in their fundamental mode. If the length of the open pipe is halved and that of closed pipe is doubled, and if they are vibrating in the fundamental mode, then the number of beats produced is:

    A) 4                     

    B) 7      

    C) 2                     

    D) 8

    Correct Answer: B

    Solution :

    for closed pipe \[{{\operatorname{f}}_{c}}=\frac{1}{2}m{{v}^{2}}\] fundamental frequency for open pipe \[{{\operatorname{f}}_{\operatorname{o}}}=\frac{\operatorname{v}}{2{{\operatorname{l}}_{o}}}\]    fundamental frequency \[{{\operatorname{f}}_{o}}-{{\operatorname{f}}_{c}}=2\] \[\frac{v}{2{{l}_{o}}}-\frac{c}{4{{l}_{o}}}=2\] \[\frac{v}{4{{l}_{o}}}=2\]                                ?.(1) Case-II  \[{{\operatorname{l}}_{c}}=2{{l}_{o}}while\,\,lopen\,\,=\frac{{{l}_{o}}}{2}\] \[{{\operatorname{f}}_{c}}=\frac{v}{4\times 2{{l}_{o}}}=\frac{v}{8{{l}_{o}}}\Rightarrow {{f}_{o}}\frac{v}{2\times \frac{{{l}_{o}}}{2}}=\frac{v}{{{l}_{o}}}\] \[{{\operatorname{f}}_{o}}-{{f}_{c}}=x\] \[\frac{v}{{{l}_{o}}}-\frac{v}{8{{l}_{o}}}=x\] \[\frac{7v}{8{{l}_{o}}}=x\]                              ?.(2) X=7                             by (1) and (2)


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