Question

A photosensitive surface emits photoelectrons when red light falls on it. Will the surface emit photoelectrons when blue light is incident on it? Give reason. 

Answer 1

The photoelectrons can be emitted from a metal surface if the frequency of incident radiation is more than the threshold frequency.

\[\text { Photemission took place when red light is incident on the photosensitive surface} . \]

\[\text { This means that }\]

\[\text { Work function of the surface } (W) < h \nu_{red} \]

\[\text { or }, W < \frac{hc}{\lambda_{red}} . . . . . (i)\]

\[\text { When blue colour light is incident on the surface, then energy imparted to electrons }\]

\[E = \frac{hc}{\lambda_{blue}} \]

\[As \lambda_{red} > \lambda_{blue} \]

\[\text { So,} \frac{hc}{\lambda_{blue}} > \frac{hc}{\lambda_{red}} . . . . . (ii)\]

\[\text { From equation (i) and (ii)}\]

\[\frac{hc}{\lambda_{blue}} > W\]

\[\text { So, photoelectrons will be emitted when blue light is incident on the photosensitive surface }. \]