JEE Main & Advanced Physics Alternating Current / प्रत्यावर्ती धारा Question Bank Critical Thinking

  • question_answer
    An alternating e.m.f. of angular frequency \[\omega \] is applied across an inductance. The instantaneous power developed in the circuit has an angular frequency [Roorkee 1999]

    A)            \[\frac{\omega }{4}\]       

    B)            \[\frac{\omega }{2}\]

    C)            \[\omega \]                          

    D)            \[2\omega \]

    Correct Answer: D

    Solution :

                       The instantaneous values of emf and current in inductive circuit are given by \[E={{E}_{0}}\sin \omega t\]and \[i={{i}_{0}}\sin \left( \omega t-\frac{\pi }{2} \right)\]respectively. So, \[{{P}_{inst}}=Ei={{E}_{0}}\sin \omega t\times {{i}_{0}}\sin \left( \omega t-\frac{\pi }{2} \right)\] \[={{E}_{0}}{{i}_{0}}\sin \omega t\left( \sin \omega t\cos \frac{\pi }{2}-\cos \omega t\sin \frac{\pi }{2} \right)\] \[={{E}_{0}}{{i}_{0}}\sin \omega t\ \cos \omega t\] \[=\frac{1}{2}{{E}_{0}}{{i}_{0}}\sin 2\omega t\]                                  \[(\sin 2\omega t=2\sin \omega t\ \cos \omega t)\] Hence, angular frequency of instantaneous power is \[2\omega \].


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