AMU Medical AMU Solved Paper-1999

  • question_answer
    A monochromatic light beam of wavelength 2537 A is falling normally on a metal plate. If the maximum velocity of emitted photoelectron is \[1.6\times {{10}^{5}}m/sec\] and a constant magnetic field of strength \[{{10}^{-4}}\] \[weber/{{m}^{2}}\]is applied parallel to metal surface, the radius of the largest circular path of photoelectrons is

    A)  0.61 m           

    B)  0.61 cm

    C)  \[6.1\times {{10}^{-4}}m\]      

    D)  \[6.1\times {{10}^{-5}}m\]

    Correct Answer: A

    Solution :

    : For photoelectron emission, \[\frac{hc}{\lambda }=\frac{1}{2}m{{v}^{2}}\] For circular motion of electron in magnetic field B, \[Bev=\frac{m{{v}^{2}}}{r}\] or \[Bev=\frac{2hc}{\lambda r}\]or\[r=\frac{2hc}{\lambda Bev}\] \[r=\frac{2\times (6.6\times {{10}^{-34}})\times (3\times {{10}^{8}})}{(2537\times {{10}^{-10}})\times (1.6\times {{10}^{-19}})\times (1.6\times {{10}^{5}})}\] \[=\frac{2\times 6.6\times 3\times 100}{2537\times 1.6\times 1.6}\] \[\therefore \]radius = 0.61 m.


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