NEET Physics Atomic Physics NEET PYQ-Atomic Physics

  • question_answer
    The energy of a photon of light is 3 eV. Then the wavelength of photon must be:                     [AIPMT 2000]

    A)          4125 nm

    B)     412.5 nm

    C)  41250 nm

    D)           4 nm  

    Correct Answer: B

    Solution :

    If energy E is expressed in eV and wavelength \[\lambda \] (in\[\overset{o}{\mathop{A}}\,\]), then energy of photon,
    \[E=\frac{12375\,}{\lambda \,({\AA})}eV\]
    \[\therefore \]      \[\lambda =\frac{12375}{E\,(eV)}{\AA}\]           
    \[=\frac{12375\,}{3\,eV}{\AA}\,-4125\,{\AA}=412.5\,nm\]
    Note:    Energy of photon is
    \[E=\frac{hc}{\lambda (\overset{o}{\mathop{\text{A}}}\,)}=\frac{12375}{\lambda (\overset{o}{\mathop{\text{A}}}\,)}eV\]
    Here, \[hc=12375\] comes from the following procedure:
                \[hc=\] (Planck’s constant) velocity of light)
    \[=\frac{(6.6\times {{10}^{-34}}J-s)\,(3\times {{10}^{8}}\,m/s)}{(1.6\times {{10}^{-19}}\,J/eV)}\]
    \[=12.375\times {{10}^{-7}}\,\,eV-m=12375\,eV-\overset{o}{\mathop{A}}\,\]


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