JCECE Engineering JCECE Engineering Solved Paper-2004

  • question_answer
    A sings with a frequency \[(n)\] and \[B\] sings with a frequency \[1/8\] that of \[A\]. If the energy remains the same and the amplitude of \[A\] is \[a,\] the amplitude of \[B\] will be:

    A) \[2a\]                                   

    B) \[8a\]

    C) \[4a\]                                   

    D)  \[a\]

    Correct Answer: B

    Solution :

    The energy \[(E)\] of a wave of amplitude \[a\], and angular velocity \[\omega \] is                 \[E=\frac{1}{2}m{{a}^{2}}{{\omega }^{2}}\] Also,      \[\omega =2\pi n\] \[\therefore \]  \[E=\frac{1}{2}m{{a}^{2}}{{(2\pi n)}^{2}}=2m\,\,{{a}^{2}}{{\pi }^{2}}{{n}^{2}}\] \[\therefore \]  \[\frac{{{E}_{A}}}{{{E}_{B}}}=\frac{{{({{a}_{A}}{{n}_{A}})}^{2}}}{{{({{a}_{B}}{{n}_{B}})}^{2}}}\] Given,   \[{{E}_{A}}={{E}_{B}},\,\,{{n}_{A}}=n,\,\,{{n}_{B}}=\frac{n}{8}\] \[\therefore \]  \[1=\frac{a_{A}^{2}\times 64{{n}^{2}}}{a_{B}^{2}{{n}^{2}}}\] \[\Rightarrow \]               \[{{a}_{B}}=8{{a}_{A}}=8a\]


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