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12th Class Physics Electrostatics & Capacitance Question Bank MCQ - Electrostatic Potential and Capacitance

  • question_answer
    Two point charges \[+10\mu C\] and \[-10\,\mu \,C\] are separated by a distance of 2 cm in water of dielectric constant 80. The potential energy of the system is:

    A) - 45 J               

    B) - 0. 56

    C) + 45 J             

    D) + 0.56 J

    Correct Answer: B

    Solution :

    (b) -0.56J Potential energy, \[U=\frac{1}{4\pi {{\varepsilon }_{0}}}\frac{{{q}_{1}}{{q}_{2}}}{r}\] \[=9\times {{10}^{9}}\times \frac{10\times {{10}^{-6}}\times -10\times {{10}^{-6}}}{2\times {{10}^{-2}}}\] \[=-\frac{9}{2}\times {{10}^{9}}\times {{10}^{-12}}\times {{10}^{4}}\] \[=-45\,J\] Due to dielectric, potential energy \[=\frac{U}{k}=-\frac{45}{80}=-0.56\,J\]


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