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  5. Fluid Mechanics, Surface Tension & Viscosity / द्रव यांत्रिकी, भूतल तनाव और चिपचिपापन

JEE Main & Advanced Physics Fluid Mechanics, Surface Tension & Viscosity / द्रव यांत्रिकी, भूतल तनाव और चिपचिपापन JEE PYQ-Fluid Mechanics, Surface Tension and Viscosity

  • question_answer
    A surface of certain metal is first illuminated with light of wavelength \[{{\lambda}_{1}}=350\,nm\] nm and then, by light of wavelength \[{{\lambda }_{2}}=540nm\]. It is found that the maximum speed of the photo electrons in the two cases differ by a factor of 2. The work function of the metal (in eV) is close to: (Energy of photon \[=\frac{1240}{\lambda \,(in\,\,nm)}\,e\,V)\]                                                                                    [JEE Main 09-Jan-2019 Morning]

    A)        5.6                              

    B)  2.5

    C) 1.8

    D)                   1.4

    Correct Answer: C

    Solution :

    [c] \[{{k}_{1}}\,\,=\,\,\frac{1240}{350}\,-\,W\,\,=\,\,3.54\,\,-\,\,W\]
                \[{{k}_{2}}\,\,=\,\,\frac{1240}{540}-W\,\,\,=\,\,2.3\,\,-\,\,W\]
                \[\frac{{{k}_{1}}}{{{k}_{2}}}\,=\,\frac{3.5u\,\,-\,\,W}{2.3\,-\,W}\,\,=\,\,\frac{4}{1}\]
                \[3.54\,\,-W\,\,=\,\,9.2\,\,-\,\,uW\]
                \[3W\,\,=\,\,5.66\,\,\]
                \[W\,\,=\,\,1.8\,eV\,\,\]
                Option [c]


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