12th Class Physics Electrostatics & Capacitance Question Bank Case Based (MCQs) - Electric Potential and Capacitance

  • question_answer
    Directions: (21-25)
    Electric Potential Energy
    This energy possessed by a system of charges by virtue of their positions. When two like charges lie infinite distance apart, their potential energy is zero because no work has to be done in moving one charge at infinite distance from the other.
    In carrying a charge q from point B, work done \[W=q\left( {{V}_{A}}-{{V}_{B}} \right)\] This work may appear as charge in KE/PE of the charge. The potential energy of two charges \[{{q}_{1}}\] and \[{{q}_{2}}\] at a distance r in air is \[\frac{{{q}_{1}}{{q}_{2}}}{4\pi {{\varepsilon }_{0}}r}\]. It is measured in joule. It may be positive, negative or zero depending on the signs of \[{{q}_{1}}\] and \[{{q}_{2}}\].
    Calculate work done in separating two electrons from a distance of 1 m to 2 m in air, where e is electric charge and k is electrostatic force constant.

    A) \[k{{e}^{2}}\]

    B) \[{{e}^{2}}/2\]

    C) \[-k{{e}^{2}}/2\]

    D) zero

    Correct Answer: C

    Solution :

    \[W={{\left( P.E. \right)}_{final}}-{{\left( P.E. \right)}_{initial}}\] \[=\frac{k{{e}^{2}}}{2}-\frac{k{{e}^{2}}}{1}=\frac{-k{{e}^{2}}}{2}\]


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