JEE Main & Advanced Physics Electrostatics & Capacitance JEE PYQ-Electrostatics and Capacitance

  • question_answer
    The electric field in a region of space is given by, \[\vec{E}={{E}_{o}}\hat{i}+2{{E}_{o}}\hat{j}\]where \[{{E}_{o}}=100N/C.\]The flux of the field through a circular surface of radius 0.02 m parallel to the YZ plane is nearly:            [JEE ONLINE 19-04-2014]

    A) 0.125 Nm2/C

    B) 0.02 Nm2/C

    C) 0.005 Nm2/C    

    D) 3.14 Nm2/C

    Correct Answer: A

    Solution :

    [a] \[\overset{\to }{\mathop{E}}\,={{E}_{0}}\hat{i}+2{{E}_{0}}\hat{j}\]
    Given, \[{{E}_{0}}=100N/c\]
    So, \[\overset{\to }{\mathop{E}}\,=100\hat{i}+200\hat{j}\]
    Radius of circular surface = 0.02 m
    Area \[=\pi {{r}^{2}}=\frac{22}{7}\times 0.02\times 0.02\]
    \[=1.25\times {{10}^{-3}}\hat{i}\,{{m}^{2}}\][Loop is parallel to Y-Z plane]
    Now, flux \[(\phi )=EA\cos \theta \]
    \[=\left( 100\hat{i}+200\hat{j} \right).1.25\times {{10}^{-3}}\hat{i}\cos {{\theta }^{o}}[\theta ={{0}^{o}}]\]
    \[=1.25\times {{10}^{-3}}N\,{{m}^{2}}/c\]
    \[=0.125N\,{{m}^{2}}/c\]


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