BCECE Engineering BCECE Engineering Solved Paper-2007

  • question_answer
    Sound waves of \[f=600\,Hz\]fall normally on a perfectly reflecting wall. The shortest distance from the wall at which all particles will have maximum amplitude of vibration will be (speed of sound = 300 m/s)

    A)  \[\frac{7}{8}m\]                              

    B)  \[\frac{3}{8}m\]                              

    C)  \[\frac{1}{8}m\]                              

    D)         \[\frac{1}{4}m\]

    Correct Answer: C

    Solution :

    Key Idea: Amplitude 15 maximum at antinode. The wall acts like a rigid boundary and reflect this wave and sends it back towards the open end. At the open end an antinode is formed and a node is formed at the wall. The distance between antinode and node is\[\frac{\lambda }{4}.\] Therefore, if n be the frequency of note emitted then                                 \[\lambda =\frac{v}{n}\]                 \[\Rightarrow \]               \[\lambda =\frac{300}{600}=\frac{1}{2}m\]          Maximum amplitude is obtained at distance                                 \[=\frac{\lambda }{4}=\frac{1}{2}\times \frac{1}{4}=\frac{1}{8}m\]          


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