BHU PMT BHU PMT (Mains) Solved Paper-2010

  • question_answer
    A charged oil drop is suspended in a uniform electric field of\[3\times {{10}^{4}}V/m\]so that it neither falls nor rises. The charge on the drop will be (take the mass of the drop is\[9.9\times {{10}^{-15}}kg\] And\[g=10m{{s}^{-2}}\])

    A) \[3.3\times {{10}^{18}}C\]           

    B) \[3.2\times {{10}^{-18}}C\]

    C)  \[1.6\times {{10}^{-18}}C\]        

    D) \[4.8\times {{10}^{-18}}C\]

    Correct Answer: A

    Solution :

                     Because the drop neither falls nor rises, so it remains stationary, then For equilibrium position, the electric farce\[qE\]will be equal to the weight of the drop. So, \[qE=mg\]                 \[q=\frac{mg}{E}\]                 \[=\frac{(9.9\times {{10}^{-15}})\times 10}{3\times {{10}^{4}}}\]                 \[=3.3\times {{10}^{-18}}C\]


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