Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2010

  • question_answer
      Two spheres A and B of radii a and b respectively are at the same potential. The ratio of the surface charge densities of A to B is

    A) \[\frac{a}{b}\]                                  

    B) \[\frac{b}{a}\]

    C) \[\frac{{{a}^{2}}}{{{b}^{2}}}\]                                    

    D) \[\frac{{{b}^{2}}}{{{a}^{2}}}\]

    Correct Answer: B

    Solution :

    Given, electric potentials of spheres are same ie, \[{{V}_{A}}={{V}_{B}}\]                 \[\Rightarrow \]               \[\frac{1}{4\pi {{\varepsilon }_{0}}}.\frac{{{q}_{1}}}{a}=\frac{1}{4\pi {{\varepsilon }_{0}}}.\frac{{{q}_{2}}}{b}\] \[\Rightarrow \]               \[\frac{{{q}_{1}}}{{{q}_{2}}}=\frac{a}{b}\]                             ?.(i) As surface charge density                 \[\sigma =\frac{q}{4\pi \,{{r}^{2}}}\] \[\Rightarrow \]               \[\frac{{{\sigma }_{1}}}{{{\sigma }_{2}}}=\frac{{{q}_{1}}}{{{q}_{2}}}\times \frac{{{b}^{2}}}{{{a}^{2}}}\]                 \[=\frac{a}{b}\times \frac{{{b}^{2}}}{{{a}^{2}}}=\frac{b}{a}\]


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