BCECE Engineering BCECE Engineering Solved Paper-2015

  • question_answer
    If\[E=100\sin (100t)\] volt and\[I=100\sin \left( 100t+\frac{\pi }{3} \right)mA\]are the instantaneous voltage and current, then the             rms values of voltage and current are respectively;

    A) \[\text{7}0.\text{7 V},\text{ 7}0.\text{7 mA}\]

    B) \[~\text{6}0.\text{9 V},\text{ 69}.\text{3 mA}\]

    C) \[~\text{9}0.\text{6 V},\text{ 141}.\text{4 mA}\]    

    D) \[\text{6}0\text{ V},\text{ 7}0\text{ mA}\]

    Correct Answer: A

    Solution :

    The instantaneous voltage is \[E=100\sin (100t)\text{volt}\]                                   ? (i) Compare it with \[E={{E}_{0}}\sin (\omega t)\]volt We get \[{{\text{E}}_{\text{0}}}\text{=100 volt,  }\!\!\omega\!\!\text{  =100 rad }{{\text{s}}^{\text{-1}}}\] The rms value of voltage is \[{{\text{E}}_{\text{rms}}}\text{=}\frac{{{\text{E}}_{\text{0}}}}{\sqrt{\text{2}}}\text{=}\frac{\text{100}}{\sqrt{\text{2}}}\text{volt = 70}\text{.7V}\] The instantaneous value of current is \[\text{I = 100 sin }\left( 100t+\frac{\pi }{3} \right)\text{mA}\] Compare it with \[I={{I}_{0}}\sin (\omega t+\phi )\] We get, \[{{\text{I}}_{\text{0}}}\text{=100 mA, }\!\!\omega\!\!\text{  =100 rad }{{\text{s}}^{\text{-1}}}\] The rms value of current is \[{{\text{I}}_{\text{rms}}}\text{=}\frac{{{\text{I}}_{\text{0}}}}{\sqrt{\text{2}}}\text{=}\frac{\text{100}}{\sqrt{\text{2}}}\text{mA=70}\text{.7mA}\]  


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