WB JEE Medical WB JEE Medical Solved Paper-2006

  • question_answer
    Figure shows three spherical and equipotential surfaces A, B and C round a point charge q. The potential difference \[{{V}_{A}}-{{V}_{B}}={{V}_{B}}-{{V}_{C}}.\]If \[{{t}_{1}}\]and \[{{t}_{2}}\] be the distance between them. Then:

    A)  \[{{t}_{1}}={{t}_{2}}\]                   

    B)  \[{{t}_{1}}>{{t}_{2}}\]

    C)  \[{{t}_{1}}<{{t}_{2}}\]                   

    D)  \[{{t}_{1}}\le {{t}_{2}}\]

    Correct Answer: C

    Solution :

                     Potential difference between two equipotential surfaces A and B, \[{{V}_{A}}-{{V}_{B}}=kq\left( \frac{1}{{{r}_{A}}}-\frac{1}{{{r}_{B}}} \right)\] \[=kq\left( \frac{{{r}_{B}}-{{r}_{A}}}{{{r}_{A}}{{r}_{B}}} \right)\] \[=\frac{kq{{t}_{1}}}{{{r}_{A}}{{r}_{B}}}\]                 or            \[{{t}_{1}}=\frac{({{V}_{A}}-{{V}_{B}}){{r}_{A}}{{r}_{B}}}{kq}\]                 or            \[{{t}_{1}}\propto {{r}_{A}}{{r}_{B}}\]                 Similarly, \[{{t}_{2}}\propto {{r}_{B}}{{r}_{C}}\]                 Since \[{{r}_{A}}<{{r}_{B}}<{{r}_{C}},\]therefore \[{{r}_{A}}{{r}_{B}}<{{r}_{B}}{{r}_{C}}\] \[\therefore \]  \[{{t}_{1}}<{{t}_{2}}\]


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