JEE Main & Advanced Physics Ray Optics Question Bank Critical Thinking

  • question_answer
    We wish to see inside an atom. Assuming the atom to have a diameter of 100 pm, this means that one must be able to resolved a width of say 10 p.m. If an electron microscope is used, the minimum electron energy required is about  [AIIMS 2004]

    A)            1.5 KeV                                   

    B)            15 KeV

    C)            150 KeV                                  

    D)            1.5 KeV

    Correct Answer: B

    Solution :

                       Wave length of the electron wave be \[10\times {{10}^{-12}}m\], Using \[\lambda =\frac{h}{\sqrt{2mE}}\]\[\Rightarrow E=\frac{{{h}^{2}}}{{{\lambda }^{2}}\times 2m}\] \[=\frac{{{(6.63\times {{10}^{-34}})}^{2}}}{{{(10\times {{10}^{-12}})}^{2}}\times 2\times 9.1\times {{10}^{-31}}}Joule\] \[=\frac{{{(6.63\times {{10}^{-34}})}^{2}}}{{{(10\times {{10}^{-12}})}^{2}}\times 2\times 9.1\times {{10}^{-31}}\times 1.6\times {{10}^{-19}}}eV\] = 15.1 KeV.


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