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AMU Medical AMU Solved Paper-2011

  • question_answer
    A charged drop of mass \[\text{3}.\text{2}\times \text{1}{{0}^{-\text{12}}}\text{ g}\]floats between two horizontal parallel plates maintained at potential difference of 980 V and separation between the plates 2 cm. The number of excess or deficient electrons on the drop is

    A)  2                                            

    B)  4

    C)  8                                            

    D)  16

    Correct Answer: D

    Solution :

                     \[m=3.2\times {{10}^{-12}}g\]                 \[=3.2\times {{10}^{-12}}\times {{10}^{-3}}kg\]                 \[=3.2\times {{10}^{-15}}kg\] Potential difference = 980 V                 \[d=2\,cm\,=2\times {{10}^{-2}}m\] Potential difference between the plates                 \[V=E\times d\]                 or            \[V=\frac{mg}{ne}\times d\]                                 \[V=\frac{mg}{ne}\times d\]                                 \[n=\frac{mg}{e\times v}\times d\]                                 \[n=\frac{3.2\times {{10}^{-15}}\times 9.8\times 2\times {{10}^{-2}}}{980\times 1.6\times {{10}^{-19}}}\]\[n=4\]


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