JEE Main & Advanced Physics Electrostatics & Capacitance NEET PYQ - Electrostatics and Capacitance

  • question_answer
    When air is replaced by a dielectric medium of constant K, the maximum force of attraction between two charges, separated by a distance: [AIPMT 1999]

    A) decreases K times

    B) increase K times

    C) remains unchanged

    D) becomes \[\frac{1}{{{K}^{2}}}\]times

    Correct Answer: A

    Solution :

    [a] According to Coulomb's law, force between two charges is directly proportional to product of charges and inversely proportional to square of distance between them. Thus,
                            \[F=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{{{q}_{1}}{{q}_{2}}}{{{r}^{2}}}\]                       …(i)
                Here, \[\frac{1}{4\pi {{\varepsilon }_{0}}}=\] proportionality constant.
                If a dielectric medium of constant K is placed between them, then new force between them,
                            \[F'=\frac{1}{4\pi {{\varepsilon }_{0}}K}.\frac{{{q}_{2}}{{q}_{2}}}{{{r}^{2}}}\]        …(ii)
                Dividing Eq. (ii) by Eq. (i), we have
                            \[\frac{F'}{F}=\frac{1}{K}\]
                or         \[F'=\frac{F}{K}\]
                Thus, new force decreases K times.


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