BCECE Engineering BCECE Engineering Solved Paper-2015

  • question_answer
    Figure given below shows a network of four capacitors of capacitance equal to \[{{C}_{1}}=C,{{C}_{2}}=2C,{{C}_{3}}\]\[=3C,{{C}_{4}}\]\[=4C\]are connected to a battery. The ratio of charges on \[{{C}_{2}}\]and \[{{C}_{4}}\] is

    A) \[7/4\]                 

    B) \[7/22\]

    C) \[3/22\]

    D) \[4/7\]

    Correct Answer: C

    Solution :

    The charge flowing through \[{{C}_{4}}\] is \[{{q}_{4}}={{C}_{4}}\times V=4{{C}_{V}}\] The series combination of \[{{C}_{1}}\] ,\[{{C}_{2}}\] and \[{{C}_{3}}\] \[\frac{1}{C'}=\frac{1}{C}+\frac{1}{2C}+\frac{1}{3C}\] \[\frac{1}{C'}=\frac{6+3+2}{6C}=\frac{11}{6C}\Rightarrow C'=\frac{6C}{11}\] Now, C? and \[{{C}_{4}}\] form parallel combination  giving \[C''=C'+{{C}_{4}}=\frac{6C}{11}+4C=\frac{50C}{11}\] Net charge,       \[q=C''V=\frac{50}{11}CV\] Total charge flowing through \[{{C}_{1}}\], \[{{C}_{2}}\] and \[{{C}_{3}}\] will be \[q'=q-{{q}_{4}}=\frac{50}{11}CV-4CV=\frac{6CV}{11}\] Since, \[{{C}_{1}}\]\[{{C}_{2}}\],\[{{C}_{3}}\]are in series combination. Hence. charge flowing through these will be same. Hence,                  \[{{q}_{2}}={{q}_{1}}={{q}_{3}}=q'=\frac{6CV}{11}\] Thus,                     \[\frac{{{q}_{2}}}{{{q}_{4}}}=\frac{6CV/11}{4CV}=\frac{3}{22}\]                  


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