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BHU PMT BHU PMT (Screening) Solved Paper-2010

  • question_answer
    Two instruments having stretched strings are being played in unison. When the tension in one of the instruments is increased by 1%, 3 beats are produced in 2 s. The initial frequency of vibration of each wire is

    A)  600 Hz                                 

    B)  300 Hz

    C)  200 Hz                                 

    D)  150 Hz

    Correct Answer: B

    Solution :

                     Initial frequency of vibration                                                                                                        \[v\propto \sqrt{T}\] When the tension in one of the instruments is increased by 1%, then                                                                                          \[v\propto \sqrt{1+\frac{1}{100}}\]                                                                                                               \[\therefore\]                                                       \[\frac{v'}{v}={{\left( 1+\frac{1}{100} \right)}^{1/2}}=1+\frac{1}{200}\]                                     Or                                                                                         \[\frac{v'-v}{v}=\frac{1}{200}\] Or                                                                                          \[\frac{3}{2v}=\frac{1}{200}\] or                                                                                                     \[v=300\text{ }Hz\]


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