JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2010

  • question_answer
        In circuit shown in figure if both the bulbs\[{{B}_{1}}\]and\[{{B}_{2}}\]are identical

    A)  their brightness will be same

    B)  \[{{B}_{1}}\]will be brighter than\[{{B}_{2}}\]

    C)  as frequency of supply voltage is increased, brightness of\[{{B}_{1}}\]will increase and that of\[{{B}_{2}}\]will decrease

    D)  only\[{{B}_{2}}\]will glow because the capacitor has infinite impedance

    Correct Answer: C

    Solution :

                    \[{{X}_{C}}=\frac{1}{\omega C}=\frac{1}{2\pi vC}\] \[=\frac{1}{2\pi \times 50\times 500\times {{10}^{-6}}}\] \[=\frac{1}{5\pi \times {{10}^{-2}}}=\frac{20}{\pi }=6.37\,\Omega \] \[{{X}_{L}}=\omega L=2\pi vL\] \[=2\pi \times 50\times 10\times {{10}^{-3}}\] \[=\pi \,\Omega =3.14\,\Omega \] As\[{{X}_{C}}>{{X}_{L}},\]so current in the lower branch will be higher, so\[{{B}_{2}}\]will glow brighter. On increasing the frequency\[{{X}_{C}}\]will decrease and \[{{X}_{L}}\]will increase, so brightness of\[{{B}_{1}}\]will increase and brightness of\[{{B}_{2}}\]will decrease.


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