JEE Main & Advanced Physics Electrostatics & Capacitance Question Bank Self Evaluation Test - Electrostatic Potential and Capacitance

  • question_answer
    The electric potential at a point (x, y, z) is given by \[V=-{{x}^{2}}y-x{{z}^{3}}+4.\] The electric field E at that point is

    A) \[\vec{E}=\hat{i}2xy+\hat{j}({{x}^{2}}+{{y}^{2}})+\hat{k}(3xz-{{y}^{2}})\]

    B) \[\vec{E}=\hat{i}{{z}^{3}}+\hat{j}xyz+\hat{k}{{z}^{2}}\]

    C) \[\vec{E}=\hat{i}(2xy-{{z}^{3}})+\hat{j}x{{y}^{2}}+\hat{k}3{{z}^{2}}x\]

    D) \[\vec{E}=\hat{i}(2xy+{{z}^{3}})+\hat{j}{{x}^{2}}+\hat{k}3x{{z}^{2}}\]

    Correct Answer: D

    Solution :

    [d] The electric field at a point is equal to negative of potential gradient at that point. \[\vec{E}=-\frac{\partial V}{\partial r}=\left[ -\frac{\partial V}{\partial x}\hat{i}-\frac{\partial V}{\partial y}\hat{j}-\frac{\partial V}{\partial z}\hat{k} \right]\] \[=\left[ (2xy+{{z}^{3}})\hat{i}+\hat{j}{{x}^{2}}+\hat{k}\,\,3x{{z}^{2}} \right]\]


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