BHU PMT BHU PMT (Mains) Solved Paper-2011

  • question_answer
    Given  that   1 kg  of  copper  contains approximately\[{{10}^{25}}\]atoms, and density of copper is\[9\times {{10}^{3}}kg/{{m}^{3}}\]. A rough estimate of the diameter of copper atom is

    A) \[2\times {{10}^{-12}}m\]           

    B) \[2\times {{10}^{-10}}m\]

    C)  \[2\times {{10}^{-14}}m\]          

    D) \[2\times {{10}^{-7}}m\]

    Correct Answer: B

    Solution :

                     Volume of 1 kg of copper \[=\frac{1}{9\times {{10}^{3}}}{{m}^{3}}\] i.e., Volume of\[{{10}^{25}}\]atoms of copper \[=\frac{1}{9\times {{10}^{3}}}{{m}^{3}}\] Volume of 1 atom of copper \[=\frac{1}{9\times {{10}^{3}}\times {{10}^{25}}}{{m}^{3}}\] \[\Rightarrow \]               \[\frac{4}{3}\pi {{r}^{3}}=\frac{1}{9\times {{10}^{28}}}\] \[\Rightarrow \]               \[{{r}^{3}}=\frac{3}{4\pi \times 9\times {{10}^{28}}}\] \[\Rightarrow \]               \[{{r}^{3}}=\frac{3}{4\times 3.14\times 3\times {{10}^{28}}}\]                 \[r=\sqrt[3]{\frac{1}{4\times 3.14\times 3\times {{10}^{28}}}}\] \[\Rightarrow \]               \[r=\frac{1}{7.2\times {{10}^{9}}}\]


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