JEE Main & Advanced Physics Photo Electric Effect, X- Rays & Matter Waves Question Bank Critical Thinking

  • question_answer
    Work function of lithium and copper are respectively 2.3 eV and 4.0 eV. Which one of the metal will be useful for the photoelectric cell working with visible light? (h = 6.6 ´ 10?34 J-s, c = 3 ´ 108 m/s)                                   [DPMT 2003]

    A)            Lithium                                   

    B)            Copper

    C)            Both                                        

    D)            None of these 

    Correct Answer: A

    Solution :

                       From \[{{\lambda }_{0}}=\frac{12375}{{{W}_{0}}}\]                          The maximum wavelength of light required for the photoelectron emission, \[{{({{\lambda }_{0}})}_{Li}}=\frac{12375}{2.3}=5380{\AA}\]. Similarly \[{{({{\lambda }_{0}})}_{Cu}}=\frac{12375}{4}\]= 3094 Å. Since the wavelength 3094 Å does not in the visible region, but it is in the ultraviolet region. Hence to work with visible light, lithium metal will be used for photoelectric cell.


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