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CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2004

  • question_answer
    Threshold wavelength for photoelectric emission from a metal surface is \[5200\text{ }\overset{o}{\mathop{A}}\,\]. Photoelectrons will be emitted when this surface is illuminated with monochromatic radiation from:

    A)  1 W IR lamp      

    B)  50 W UV lamp

    C)  50 W IR lamp    

    D)  10 W IR lamp

    Correct Answer: B

    Solution :

    For photoelectric emission to take place the wavelength of incident light must be less than the threshold value which is given as \[5200\overset{o}{\mathop{A}}\,\]. The wavelength of infra-red light \[=7800\overset{o}{\mathop{A}}\,\] The wavelength of ultra-violet light \[=4000\overset{o}{\mathop{A}}\,\] Thus, it is obvious that wavelength of UV   radiation is less than the threshold value.   Hence, it can emit photoelectrons from the surface of metal.


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