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JEE Main & Advanced Sample Paper JEE Main - Mock Test - 12

  • question_answer
    When light of \[520\text{ }nm\]wavelength falls on a metal, which of the following metals will show photoelectric effect. The work function \[(\phi )\]of some metals are given below:
    Metal \[Li\] \[Na\] \[K\] \[Mg\]
    \[\phi (\,eV)\] \[2.4\] \[2.3\] \[2.2\] \[3.7\]

    A) \[Li.Na\]                

    B)   \[Na,K\]     

    C) \[Li,\,\,K\]                 

    D)    \[K,\text{ }Mg\]

    Correct Answer: B

    Solution :

      [b] Since the value of \[hc=1240\text{ }eV\text{ }nm.\] Energy corresponding to \[\lambda =500\text{ }nm\]is: \[\frac{1240\,eV\,nm}{520\,nm}=2.38\,eV\] Element having \[\phi <2.38\,eV\]will show photoelectric effect, are \[Na(2.3)\] and \[K(2.2)\] Hence option is (2)        


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