NEET AIPMT SOLVED PAPER 2000

  • question_answer
                    A sonometer wire when vibrated in full length has frequency n. Now it is divided by the help of bridges into a number of segments of lengths \[{{l}_{1}},\,{{l}_{2}},\,{{l}_{3}}...\]. When vibrated these segments have frequencies \[{{n}_{1}},\,{{n}_{2}},\,{{n}_{3}},....\]then the correct relation is:

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

    B)                 \[{{n}^{2}}=n_{1}^{2}+n_{2}^{2}+n_{3}^{2}+...\]

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

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

    Correct Answer: C

    Solution :

                    From law of length, the frequency of vibrating string is inversely proportional to its length, i.e.,                 \[n\propto \frac{1}{l}\] or            \[nl=\] constant (say k) or           \[nl=k\]   or  \[l=\frac{k}{n}\]                 The segment of string of length \[{{l}_{1}},\,{{l}_{2}},\,{{l}_{3}}...\]                 have frequencies \[{{n}_{1}},{{n}_{2}},{{n}_{3}}\,,....\]                 Total length of string is \[l\].                 So,          \[l={{l}_{1}}+{{l}_{2}}+{{l}_{3}}+...\]                 \[\therefore \frac{k}{n}=\frac{k}{{{n}_{1}}}+\frac{k}{{{n}_{2}}}+\frac{k}{{{n}_{3}}}+.....\]                 \[or\frac{1}{n}=\frac{1}{{{n}_{1}}}+\frac{1}{{{n}_{2}}}+\frac{1}{{{n}_{3}}}+....\]


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