AFMC AFMC Solved Paper-2011

  • question_answer
    When the wavelength of sound changes from 1 m to 1.01 m, the number of beats heard are 4. The velocity of sound is

    A) 404 m/s                               

    B) 4.04 m/s

    C) 414 m/s                                               

    D) 400 m/s

    Correct Answer: A

    Solution :

    Let \[{{n}_{1}}\]and \[{{n}_{2}}\]be the frequencies of the two notes of wavelengths \[{{\lambda }_{1}}\] and \[{{\lambda }_{2}}.\] Here, \[{{\lambda }_{1}}=1\,m,{{\lambda }_{2}}=1.01\,m\] If v is velocity of sound, then \[{{n}_{1}}=\frac{v}{1}\]and \[{{n}_{2}}=\frac{v}{1.01}\] If the number of beats produced per second is b, then \[b={{n}_{1}}-{{n}_{2}}\] \[4=\frac{v}{1}-\frac{v}{1.01}\] \[\therefore \] \[v=\frac{4.04}{0.01}=404\,m/s\]


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