NEET Physics Electrostatics & Capacitance Question Bank NEET PYQ - Electrostatics and Capacitance

  • question_answer
    The electric potential at a point \[(x,\text{ }y,\text{ }z)\] is given by \[V=-{{x}^{2}}\,y-x{{z}^{3}}+4\] The electric field \[\vec{E}\] at that point is [AIPMT (S) 2009]

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

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

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

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

    Correct Answer: A

    Solution :

    [a] Key Idea Electric field at a point is equal to the negative gradient of the electrostatic potential at that point.                 
    Potential gradient relates with electric field according to the following relation \[E=\frac{-dV}{dr}\]
    \[\vec{E}=-\frac{\partial \,V}{\partial \,r}=\left[ -\frac{\partial \,V}{\partial \,x}\hat{i}-\frac{\partial \,V}{\partial \,y}\hat{j}-\frac{\partial \,V}{\partial x}\hat{k} \right]\]
    \[=[\hat{i}\,(2xy+{{z}^{3}})+\hat{j}\,{{x}^{2}}+\hat{k}\,3x{{z}^{2}}]\]


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