J & K CET Engineering J and K - CET Engineering Solved Paper-2003

  • question_answer
    When  light  of wavelength  \[300~nm\](nanometer) falls on a photoelectric emitter, photoelectrons are just liberated. For another emitter, however, light of \[600\text{ }nm\]wavelength is sufficient for creating photoemission. What is the ratio of the work function of the two emitters?

    A)  \[1:2\]        

    B)  \[2:1\]

    C)  \[4:1\]       

    D)  \[1:4\]

    Correct Answer: B

    Solution :

    The minimum energy required for the emission of photoelectrons from a metal is called the work function of that metal. Given by \[W=hv\]                   ...(i) where v is threshold frequency and h is Planck's constant. Also,             \[v=\frac{c}{\lambda }\] ?..(ii) where c is speed of light and X the threshold wavelength. From Eqs. (i) and (ii), we get \[W=\frac{hc}{\lambda }\] Given, \[{{\lambda }_{1}}=300nm,\,\,\,\,{{\lambda }_{2}}=600nm.\] \[\therefore \] \[\frac{{{\lambda }_{2}}}{{{\lambda }_{1}}}=\frac{{{W}_{1}}}{{{W}_{2}}}\] \[\Rightarrow \] \[\frac{{{W}_{1}}}{{{W}_{2}}}=\frac{600}{300}=\frac{2}{1}\]


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