JIPMER Jipmer Medical Solved Paper-2008

  • question_answer
    Hard X-rays for the study of fractures in bones should have a minimum wavelength of \[{{10}^{-11}}\] m. The accelerating voltage for electrons in X-ray machine should be:

    A) \[\text{124}\,\text{kV}\]                             

    B) \[\text{124}\,\text{kV}\]

    C) between 60 \[\text{kV}\]and 70\[\text{kV}\]

    D) \[=100\,\text{kV}\]

    Correct Answer: A

    Solution :

    From conservation of energy the kinetic energy of electron equals the maximum photon energy (we neglect the work function \[\phi \] because it is normally so small compared to\[e{{V}_{0}}\]). \[\therefore \]  \[e{{V}_{0}}=h{{v}_{\max }}\] or            \[e{{V}_{0}}=\frac{hc}{{{\lambda }_{\min }}}\] \[\therefore \]  \[{{V}_{0}}=\frac{hc}{e{{\lambda }_{\min }}}\] or            \[{{V}_{0}}=\frac{12400\times {{10}^{-10}}}{{{10}^{-11}}}\]      \[=124\,kV\] Hence, accelerating voltage for electrons in X-ray machine should be less than 124 kV.


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