KVPY Sample Paper KVPY Stream-SX Model Paper-17

  • question_answer
    A parallel palate capacitor with square plates is filled with four dielectrics of dielectric constants \[{{K}_{1,}}\]\[{{K}_{2,}}\]\[{{K}_{3,}}\] \[{{K}_{4,}}\] arranged as shown in the figure. The effective dielectric constant K will be:
    \[{{K}_{1}}\] \[{{K}_{2}}\] L/2
    \[{{K}_{3}}\] \[{{K}_{4}}\] L/2
    \[\leftarrow d/2\to \leftarrow d/2\to \]

    A) \[K=\frac{({{K}_{1}}+{{K}_{3}})\,({{K}_{2}}+K4)}{{{K}_{1}}+{{K}_{2}}+{{K}_{3}}+{{K}_{4}}}\]

    B) \[K=\frac{({{K}_{1}}+{{K}_{2}})\,({{K}_{3}}+{{K}_{4}})}{2\,({{K}_{1}}+{{K}_{2}}+{{K}_{3}}+{{K}_{4}})}\]

    C) \[K=\frac{({{K}_{1}}+{{K}_{2}})\,({{K}_{3}}+{{K}_{4}})}{{{K}_{1}}+{{K}_{2}}+{{K}_{3}}+{{K}_{4}}}\]

    D) \[K=\frac{({{K}_{1}}+{{K}_{4}})\,({{K}_{2}}+{{K}_{3}})}{2\,({{K}_{1}}+{{K}_{2}}+{{K}_{3}}+{{K}_{4}})}\]

    Correct Answer: A

    Solution :

    \[{{C}_{1}}=\frac{{{\varepsilon }_{0}}{{K}_{1}}\frac{{{L}^{2}}}{2}}{\frac{d}{2}}+\frac{{{\varepsilon }_{0}}{{K}_{3}}\frac{{{L}^{2}}}{2}}{\left( \frac{d}{2} \right)}\]\[=\frac{{{\varepsilon }_{0}}{{L}^{2}}}{d}({{K}_{1}}+{{K}_{3}})\]
    \[{{C}_{2}}=\frac{{{\varepsilon }_{0}}{{K}_{2}}\frac{{{L}^{2}}}{L}}{\frac{d}{2}}+\frac{{{\varepsilon }_{0}}{{K}_{4}}\frac{{{L}^{2}}}{2}}{\frac{d}{2}}\]\[=\frac{{{\varepsilon }_{0}}{{L}^{2}}}{d}({{K}_{2}}+{{K}_{4}})\]
    \[\therefore \]      \[\frac{1}{c}=\frac{1}{c}+\frac{1}{{{c}^{2}}}\]
    \[\Rightarrow \]   \[\frac{d}{{{\varepsilon }_{0}}K{{L}^{2}}}=\frac{d}{{{\varepsilon }_{0}}{{L}^{2}}({{K}_{1}}+{{K}_{3}})}+\frac{d}{{{\varepsilon }_{0}}{{L}^{2}}({{K}_{2}}+{{K}_{4}})}.\]


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