JCECE Engineering JCECE Engineering Solved Paper-2011

  • question_answer
    The \[80\,\,\Omega \] galvanometer deflects full scale for a potentials of\[20\,\,mV\]. A voltmeter deflecting full scale of \[5\,\,V\] is to made using this galvanometer. We must connect

    A)  a resistance of \[19.92\,\,k\Omega \] parallel to the galvanometer

    B)  assistance of \[19.92\,\,k\Omega \] in series with the galvanometer

    C)   a resistance of \[20\,\,k\Omega \] parallel to the galvanometer

    D)   a resistance of \[20\,\,k\Omega \] in series with galvanometer

    Correct Answer: B

    Solution :

    The current through galvanometer producing full scale deflection is                 \[I=\frac{V}{R}=\frac{20\times {{10}^{-3}}}{80}=2.5\times {{10}^{-4}}A\] To convert galvanometer into a voltmeter, a high resistance is connected in series with the galvanometer                 \[5=(2.5\times {{10}^{-4}})(R+80)\]                 \[R=19.92\,\,k\Omega \]


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