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CET Karnataka Medical CET - Karnataka Medical Solved Paper-2004

  • question_answer
    Threshold wavelength for photoelectric emission from a metal surface is \[5200\overset{\text{o}}{\mathop{\text{A}}}\,\]. 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 \[5200{\AA}.\]. The wavelength of infra-red light \[=7800{\AA}\] The wavelength of ultra-violet light\[=4000{\AA}\] 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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