JEE Main & Advanced Physics Alternating Current / प्रत्यावर्ती धारा Question Bank Self Evaluation Test - Alternating Current

  • question_answer
    An inductor 20 mH, a capacitor \[50\,\mu F\]and a resistor \[40\Omega \] are connected in series across a source of emf V=10 sin 340 t. The power loss in A.C. circuit is:

    A) 0.51 W  

    B) 0.67 W

    C) 0.76 W

    D) 0.89 W

    Correct Answer: A

    Solution :

    [a] Given: L=20mH; \[C=50\mu F\]; \[R=40\Omega \] \[V=10\,\sin \,340\,t\]                  \[\therefore \,\,\,{{V}_{runs}}=\frac{10}{\sqrt{2}}\] \[{{X}_{C}}=\frac{1}{\omega C}=\frac{1}{340\times 50\times {{10}^{-6}}}=58.8\Omega \] \[{{X}_{L}}=\omega L=340\times 20\times {{10}^{-3}}=6.8\Omega \]  Impedance, \[Z=\sqrt{{{R}^{2}}+{{({{X}_{C}}-{{X}_{L}})}^{2}}}\] \[=\sqrt{{{40}^{2}}+{{(58.8-6.8)}^{2}}}=\sqrt{4304}\,\Omega \] Power loss in A.C. circuit, \[P=i_{rms}^{2}R={{\left( \frac{{{V}_{rms}}}{Z} \right)}^{2}}\] \[R={{\left( \frac{10/\sqrt{2}}{\sqrt{4304}} \right)}^{2}}\times 40\] \[=\frac{50\times 40}{4304}\simeq 0.51\,W\]


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