question_answer

For a photosensitive surface, threshold wavelength is \[{{\lambda }_{0}}\]. Does photo-emission occur if the wavelength \[(\lambda )\] of the incident radiation is (i) more than\[{{\lambda }_{0}}\] (ii) less than \[{{\lambda }_{0}}\]? Justify your answer.           

Answer:

                The maximum kinetic energy of the photo-electron is \[{{K}_{\max }}=\frac{hc}{\lambda }-\frac{hc}{{{\lambda }_{0}}}=hc\left( \frac{{{\lambda }_{0}}-\lambda }{\lambda {{\lambda }_{0}}} \right)\] (i) When \[\lambda >{{\lambda }_{0}},\]the kinetic energy of the photo- electron is negative. The photo-electric emission does not occur. (ii) When\[\lambda <{{\lambda }_{0}}\], the kinetic energy of the electron is positive. The photo-electric emission will occur.