NEET Physics Wave Mechanics NEET PYQ-Wave Mechanics

  • question_answer
    A tuning fork of frequency 512 Hz makes 4 beats/s with the vibrating string of a piano. The beat frequency decreases to 2 beats/s when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was                                                                                                                    [AIPMT (S) 2010]

    A)  510 Hz            

    B)       514 Hz

    C)  516 Hz

    D)       508 Hz

    Correct Answer: D

    Solution :

    Suppose \[{{n}_{p}}=\] frequency of piano = ?
    \[({{n}_{p}}\propto \sqrt{T})\] \[{{n}_{f}}=\] frequency of tuning fork \[=512\text{ }Hz\,\,x=\] Beat frequency = 4 beats/s, which is decreasing \[(4\to 2)\] after changing the tension of piano wire. Also, tension of piano wire is increasing so \[{{n}_{p}}\uparrow \]
    Hence,  \[{{n}_{p}}\uparrow -{{n}_{f}}=x\downarrow \xrightarrow[{}]{{}}worng\]
    \[{{n}_{p}}-{{n}_{p}}\uparrow =x\downarrow \xrightarrow[{}]{{}}correct\]
    \[\Rightarrow \]   \[{{n}_{p}}={{n}_{f}}-x=512-4=508\,Hz\]


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