JEE Main & Advanced Sample Paper JEE Main Sample Paper-9

  • question_answer
    Two concentric spheres of radii \[{{r}_{1}}\And {{r}_{2}}\]carry charges \[{{q}_{1}}\And {{q}_{2}}\]respectively. If the surface charge density \[(\sigma )\] is the same for both spheres, the electric potential at the common center will be

    A) \[\frac{\sigma }{{{\in }_{0}}}\times \frac{{{r}_{1}}}{{{r}_{2}}}\]                   

    B) \[\frac{\sigma }{{{\in }_{0}}}\times \frac{{{r}_{2}}}{{{r}_{1}}}\]

    C) \[\frac{\sigma }{{{\in }_{0}}}({{r}_{1}}-{{r}_{2}})\]                             

    D) \[\frac{\sigma }{{{\in }_{0}}}({{r}_{1}}+{{r}_{2}})\]

    Correct Answer: D

    Solution :

    Electric potential at common centre is, \[v=\frac{{{q}_{1}}}{4\pi {{\in }_{0}}{{r}_{1}}}+\frac{{{q}_{2}}}{4\pi {{\in }_{0}}{{r}_{2}}}\] \[V=\frac{\sigma }{{{\in }_{0}}}{{r}_{1}}+\frac{\sigma }{{{\in }_{0}}}\times {{r}_{2}}=\frac{\sigma }{{{\in }_{0}}}[{{r}_{1}}+{{r}_{2}}]\]\[\left[ \begin{align}   & \therefore {{q}_{1}}=4\pi r_{1}^{2}\times \sigma  \\  & {{q}_{1}}=4\pi r_{2}^{2}\times \sigma  \\ \end{align} \right]\]


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