CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2003

  • question_answer
    The capacitors A and B have identical geometry. A material with a dielectric constant 3 is present between the plates of B. The potential difference across A and B are respectively:

    A)  2.5V, 7.5 V     

    B)                         2V, 8V 

    C)         8V, 2V                 

    D)         7.5V, 2.5V

    E)  3V, 2V

    Correct Answer: D

    Solution :

    \[{{C}_{A}}=\frac{{{\varepsilon }_{0}}A}{d},{{C}_{B}}=\frac{3{{\varepsilon }_{0}}A}{d}=3{{C}_{A}}\] \[C=\frac{{{C}_{A}}\times {{C}_{B}}}{{{C}_{A}}+{{C}_{B}}}\] \[=\frac{{{C}_{A}}\times 3{{C}_{A}}}{{{C}_{A}}+3{{C}_{A}}}\] \[=\frac{3}{4}{{C}_{A}}\] \[\therefore \]Net charge                 \[q=CV=\frac{3}{4}{{C}_{A}}\times 10=7.5\,{{C}_{A}}\] Hence,                  \[{{V}_{A}}=\frac{q}{{{C}_{A}}}=7.5V\] and        \[{{V}_{B}}=\frac{q}{{{C}_{B}}}=2.5V\]


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