NEET Sample Paper NEET Sample Test Paper-70

  • question_answer
    In a detector, output circuit consists of \[\operatorname{R}=10k\Omega \]and\[\operatorname{C} = 100 \mu F\]. The frequency of carrier signal it can detect is

    A) \[>>1\,\,MHz\]

    B) \[0.1\text{ }kHz\]

    C) \[>>1\text{ }GHz\]               

    D) \[{{10}^{3}}\,Hz\]

    Correct Answer: A

    Solution :

    Here \[R=10\,k\,\Omega ={{10}^{4}}\,\Omega \] \[\operatorname{C}=100pF=1{{0}^{-10}}F\] Time constant of the circuit \[\tau \,\,=\,\,RC=1{{0}^{4}}\times {{10}^{-10}}\,\,=\,\,{{10}^{-}}^{6}\,s\] For demodulation, \[\frac{1}{{{f}_{c}}}<<RC\] Or \[{{f}_{c}}>>\frac{1}{RC}\] \[{{f}_{c}}>>\frac{1}{{{10}^{-6}}}\,\,=\,\,{{10}^{6}}\,Hz\] Therefore, frequency of carrier signal must be much greater than 1 MHz.                  


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