BHU PMT BHU PMT (Mains) Solved Paper-2007

  • question_answer
    Electric field at\[x=10\]cm is 100 V/m and at \[x=-10\]cm is\[-100\text{ }V/m\]. The magnitude of charge enclosed by the cube of side 20 m is

    A)  \[8{{\varepsilon }_{0}}\]                             

    B) \[2{{\varepsilon }_{0}}\]

    C)  \[3{{\varepsilon }_{0}}\]                             

    D) \[5{{\varepsilon }_{0}}\]

    Correct Answer: A

    Solution :

                     From Gauss's law, "the net electric flux through any closed surface is equal to the net charge inside the surface divided by \[{{\varepsilon }_{0}}\].? Then \[\mathop{\int\mkern-20.8mu \circlearrowleft}  \overrightarrow{E} .\overrightarrow{dS}=\frac{{{q}_{in}}}{{{\varepsilon }_{0}}}\] \[\therefore \]\[100\times {{(0.2)}^{2}}-(100){{(0.2)}^{2}}+0+0=\frac{{{q}_{in}}}{{{\varepsilon }_{0}}}\] \[\Rightarrow \]                               \[4-(-4)=\frac{{{q}_{in}}}{{{\varepsilon }_{0}}}\] \[\therefore \]                  \[{{q}_{in}}=8\,{{\varepsilon }_{0}}\]


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