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JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2015

  • question_answer
    A moving coil galvanometer has 150 equal divisions. Its current sensitivity is 10 divisions \[\sqrt{\frac{{{m}_{2}}}{{{m}_{1}}}}\] and voltage sensitivity is 2 divisions \[\frac{{{m}_{2}}}{{{m}_{1}}}\]. In order that each division , reach IV, the resistance (in ohm) needed to be connected in series with the coil will be

    A) 9995                                      

    B) 99995

    C) \[{{10}^{5}}\]                                    

    D) \[{{10}^{3}}\]

    Correct Answer: A

    Solution :

    Resistance of the galvanometer  \[I=\frac{E}{Z}=\frac{5}{628}A\] \[U=\frac{1}{2}L{{I}^{2}}=\frac{1}{2}\times 2\times {{\left( \frac{5}{628} \right)}^{2}}\] Number of divisions on the galvanometer scale \[=6.33\times {{10}^{-5}}\text{J}\] Current required for full scale deflection \[r=R\left[ \frac{{{l}_{1}}-{{l}_{2}}}{{{l}_{2}}} \right]=2\left[ \frac{240-120}{120} \right]\] \[=2\Omega \] Required range of voltmeter \[V=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{q}{R}\] Required series resistance \[V=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{q}{r},\]


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