JEE Main & Advanced Physics Electrostatics & Capacitance Question Bank Electric Field and Potential

  • question_answer
    The electric potential \[V\] at any point O (x, y, z all in metres) in space is given by \[V=4{{x}^{2}}\,volt\]. The electric field at the point \[(1m,\,0,\,2m)\] in \[volt/metre\] is                                                         [IIT 1992; RPET 1999; MP PMT 2001]

    A)                    8 along negative \[X-\]axis

    B)                    8 along positive \[X-\]axis

    C)                    16 along negative \[X-\]axis

    D)                    16 along positive \[Z-\]axis

    Correct Answer: A

    Solution :

                 The electric potential \[V\,(x,y,z)=4{{x}^{2}}\,volt\] Now \[\overrightarrow{E}=-\,\left( \hat{i}\frac{\partial V}{\partial x}+\hat{j}\frac{\partial V}{\partial y}+\hat{k}\frac{\partial V}{\partial z} \right)\] Now \[\frac{\partial V}{\partial x}=8x,\,\frac{\partial V}{\partial y}=0\] and \[\frac{\partial V}{\partial z}=0\] Hence \[\overrightarrow{E}=-\,8x\hat{i}\], so at point (1m, 0, 2m) \[\overrightarrow{E}=-\,8\hat{i}\,\,volt/metre\] or 8 along negative X-axis.


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