JEE Main & Advanced Physics Wave Mechanics Question Bank Self Evaluation Test - Waves

  • question_answer
    If\[{{n}_{1}}\],\[{{n}_{2}}\]and \[{{n}_{3}}\] are the fundamental frequencies of three segments into which a string is divided, then the original fundamental frequency n of the string is given by    

    A)  \[\frac{1}{n}=\frac{1}{{{n}_{1}}}+\frac{1}{{{n}_{2}}}+\frac{1}{{{n}_{3}}}\]

    B)  \[\frac{1}{\sqrt{n}}=\frac{1}{\sqrt{{{n}_{1}}}}+\frac{1}{\sqrt{{{n}_{2}}}}+\frac{1}{\sqrt{{{n}_{3}}}}\]

    C) \[\sqrt{n}=\sqrt{{{n}_{1}}}+\sqrt{{{n}_{2}}}+\sqrt{{{n}_{3}}}\]

    D) \[n={{n}_{1}}+{{n}_{2}}+{{n}_{3}}\]

    Correct Answer: A

    Solution :

    [a] Total length of string \[\ell ={{\ell }_{1}}+{{\ell }_{2}}+{{\ell }_{3}}\] (As string is divided into three segments) \[But\text{ }frequency\propto \frac{1}{length}\]          \[\,\left( \because f=\frac{1}{2\ell }\sqrt{\frac{T}{m}} \right)\] so \[\frac{1}{n}=\frac{1}{{{n}_{1}}}+\frac{1}{{{n}_{2}}}+\frac{1}{{{n}_{3}}}\].


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