NEET Physics Electrostatics & Capacitance Question Bank NEET PYQ - Electrostatics and Capacitance

  • question_answer
    The effective capacitance between points x and y of figure shown is:            [AIPMT 1999]

    A) \[6\,\mu F\]

    B) \[12\,\mu F\]

    C) \[18\,\mu F\]

    D) \[24\,\mu F\]

    Correct Answer: A

    Solution :

    [a] The given circuit can be redrawn as
                It is a balanced Wheatstone’s bridge
                            \[\left( as\frac{{{C}_{AB}}}{{{C}_{BD}}}=\frac{{{C}_{AC}}}{{{C}_{CD}}}==\frac{6}{6} \right)\]
                So, potential of B and C are equal and \[20\,\mu F\] capacitor is ineffective. The simplified circuit is shown as:
                Capacitors of \[6\,\mu F\] and \[6\,\mu F\] in upper arms are in series order, so
                            \[C'=\frac{6\times 6}{6+6}=\frac{36}{12}=3\,\mu F\]
                Similarly, \[6\,\mu F\] and \[6\,\mu F\] in lower arms are in series order, so
                            \[C''=\frac{6\times 6}{6+6}=3\mu F\]
                Now, C’ and C” are in parallel order, hence
                            \[C=C'+C''=3+3=6\,\mu F\]

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