KVPY Sample Paper KVPY Stream-SX Model Paper-1

  • question_answer
    In the figure shown \[{{V}_{1}},\]\[{{V}_{2}}\] are AC voltmeters and A is AC ammeter. The readings of \[{{V}_{1}},\]\[{{V}_{2}},\]\[{{V}_{3}}\] and A are 10V, 20V, 20V, 2A respectively. Find the values of R, C, L and the source voltage \[{{V}_{s}}.\] If the inductor is short circuit then what will be the reading of and \[{{V}_{1}},\]\[{{V}_{2}}\] A.

    A) \[2\sqrt{5}\] volts      

    B) \[4\sqrt{5}\] volts

    C) \[6\sqrt{5}\] volts                       

    D) \[8\sqrt{5}\] volts

    Correct Answer: B

    Solution :

    [B]
    Let \[{{I}_{r}}\]be the rms current through the in circuit then
    \[{{I}_{r}}=2A,\] \[\frac{{{I}_{r}}}{\omega C}=20V,\] \[\omega L=20V\] and \[{{I}_{r}}R=10V\]
    Solving we get \[R=5\Omega ,\] \[C=\frac{1}{\pi }\times {{10}^{-3}}F\] and \[L=\frac{1}{10\pi }\,\,H\]
    \[\therefore {{V}_{S}}=\]Source Voltage
    \[={{I}_{r}}\sqrt{{{R}^{2}}+{{\left( \omega L-\frac{1}{\omega C} \right)}^{2}}}\]
    \[=\sqrt{(I,{{R}^{2}})+{{\left( I{{,}_{r}}\omega L-\frac{1}{\omega C} \right)}^{2}}}\]
    \[=\sqrt{{{10}^{2}}+{{(20-20)}^{2}}}=10\,volts\]
    Now, after the inductor is shorted
    \[{{I}_{r}}=\frac{{{v}_{s}}}{\sqrt{{{R}^{2}}+\frac{1}{{{\omega }^{2}}{{C}^{2}}}}}=\frac{10}{\sqrt{25+100}}=\frac{10}{\sqrt{5}}\]
    ampere \[{{v}_{1}}={{I}_{r}}R=2\sqrt{5}\,\,volts\]
    \[{{v}_{2}}=\frac{{{I}_{r}}}{\omega C}=4\sqrt{5}\,\,volts\,\,Ans.\]


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