RAJASTHAN PMT Rajasthan - PMT Solved Paper-2007

  • question_answer
    If the electric flux entering and leaving an enclosed surface respectively are \[{{\phi }_{1}}\] and \[{{\phi }_{2,}}\] the electric charge inside the surface will be

    A)  \[\frac{{{\phi }_{2}}-{{\phi }_{1}}}{{{\varepsilon }_{0}}}\]                             

    B)  \[\frac{{{\phi }_{2}}+{{\phi }_{1}}}{{{\varepsilon }_{0}}}\]

    C)  \[\frac{{{\phi }_{1}}-{{\phi }_{2}}}{{{\varepsilon }_{0}}}\]             

    D)         \[{{\varepsilon }_{0}}({{\phi }_{1}}+{{\phi }_{2}})\]

    Correct Answer: D

    Solution :

    According to Gauss theorem, the net electric flux through any closed surface is equal to the net charge inside the surface divided by\[{{\varepsilon }_{0}}\]. Therefore,                                 \[\phi =\frac{q}{{{\varepsilon }_{0}}}\] Let \[-{{q}_{1}}\] be the charge, due to which flux \[{{\phi }_{1}}\] is entering the surface                 \[{{\phi }_{1}}=\frac{-{{q}_{1}}}{{{\varepsilon }_{0}}}\] or            \[-{{q}_{1}}={{\varepsilon }_{0}}{{\phi }_{1}}\] Let \[+{{q}_{2}}\] be the charge, due to which flux \[{{\phi }_{2}}\] is leaving the surface \[\therefore \]  \[{{\phi }_{2}}=\frac{{{q}_{2}}}{{{\varepsilon }_{0}}}\] So, electric charge inside the surface                 \[={{q}_{2}}-{{q}_{1}}\]                 \[={{\varepsilon }_{0}}{{\phi }_{2}}+{{\varepsilon }_{0}}{{\phi }_{1}}={{\varepsilon }_{0}}({{\phi }_{2}}+{{\phi }_{1}})\]


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