JEE Main & Advanced Physics Electrostatics & Capacitance Question Bank Assertion and Reason

  • question_answer
    Assertion             :       The surface charge densities of two spherical conductors of different radii are equal. Then the electric field intensities near their surface are also equal.             Reason     :   Surface charge density is equal to charge per unit area.

    A)             If both assertion and reason are true and the reason is the correct explanation of the assertion.

    B)             If both assertion and reason are true but reason is not the correct explanation of the assertion.

    C)             If assertion is true but reason is false.

    D)             If the assertion and reason both are false.

    E)                 If assertion is false but reason is true.

    Correct Answer: B

    Solution :

                As \[{{\sigma }_{1}}={{\sigma }_{2}}\] (Given) \[\therefore \] \[\frac{{{q}_{1}}}{4\pi r_{1}^{2}}=\frac{{{q}_{2}}}{4\pi r_{2}^{2}},\] or \[\frac{{{q}_{1}}}{{{q}_{2}}}=\frac{r_{1}^{2}}{r_{2}^{2}}\] [Let \[{{r}_{1}}\]and \[{{r}_{2}}\]be two different radii] Then the ratio of electric field intensities near the surface of spherical conductor, \[\frac{{{E}_{1}}}{{{E}_{2}}}=\frac{{{q}_{1}}}{4\pi {{\varepsilon }_{0}}r_{1}^{2}}\times \frac{4\pi {{\varepsilon }_{0}}r_{2}^{2}}{{{q}_{2}}}\]\[=\frac{{{q}_{1}}}{{{q}_{2}}}\times \frac{r_{2}^{2}}{r_{1}^{2}}=1\]  i.e. \[{{E}_{1}}={{E}_{2}}\] 


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