KVPY Sample Paper KVPY Stream-SX Model Paper-3

  • question_answer
    Current in an ac circuit is given by \[i=3\,\,\sin \,\,\omega \,\,t+4\,\,\cos \,\,\omega \,\,t\] then:

    A) rms value of current is 5 A.

    B) mean value of this current in one half period will be \[6/\pi .\]

    C) if voltage applied is \[V={{V}_{m}}\sin \,\,\omega \,t\] at then the circuit must be containing resistance and capacitance.

    D) if voltage applied is \[V={{V}_{m}}\sin \,\,\omega \,t,\] the circuit may contain only resistance and inductance.

    Correct Answer: C

    Solution :

    \[i=3\sin \omega \,t+4\cos \omega \,t\]
    \[=5\,\,\left[ \frac{3}{5}\sin \omega \,t+\frac{4}{5}\cos \omega \,t \right]\]
    \[=5\,[\sin \,(\omega \,t+\delta )]\]                                      ?(1)
    \[\Rightarrow \]   rms value \[=\frac{5}{\sqrt{2}}\]
    \[\Rightarrow \]   mean value \[=\frac{\int\limits_{{{T}_{1}}}^{{{T}_{2}}}{idt}}{\int\limits_{{{T}_{1}}}^{{{T}_{2}}}{dt}}\]
    \[\therefore \] Initial value is not given hence the mean value will be different for various time intervals.
    If voltage applied is \[V={{V}_{m}}\sin \omega \,t\] then i given by equation (1) indicates that it is ahead of V by \[\delta \]where \[0<\delta <90\] which indicates that the circuit contains R & C.
    Hence [c].


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