12th Class Physics Sample Paper Physics Sample Paper-7

  • question_answer
    Green light ejects photoelectrons from a given photosensitive surface whereas yellow light does not. What will happen in case of
    (i) violet, and     
    (ii) red light?
    Give reason for your answer.


    As photoelectric emission takes place for green light but does not take place for yellow light. Hence, threshold wavelength \[{{\lambda }_{0}}\] lies somewhere between them.

    (i) When incident light is of violet colour, its wavelength is even less than that of green light, i.e. \[\lambda <{{\lambda }_{0}},\] as a result, photoelectric emission will definetly take place.
    (ii) When incident light is of red colour, its wavelength is even greater than that of yellow light, i.e. \[\lambda >{{\lambda }_{0}},\] consequently, no photoelectric emission will take Place.

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