Question

Threshold wavelength of certain metal is ${\lambda }_0$. A radiation of wavelength $\lambda <{\lambda }_0$ is incident on the plate. Then, choose the correct statement from the following

• A. initially electrons will come out from the plate
• B. the ejected electrons experience retarding force due to development of positive charges on the plate
• C. after some time, ejection of electrons stops
• D. none of the above

Answer 1

Answer: (A), (B)

The correct options are
A initially electrons will come out from the plate
B the ejected electrons experience retarding force due to development of positive charges on the plate

Photo electric emission of electrons takes place when the wavelength of incident radiation is less than the threshold wavelength of the metal surface.
Since $\lambda <{\lambda }_o$ (Given)
Thus initially the electrons will come out from the plate.
The plate becomes positively charged on emission of electrons from the plate. So the plate attracts the emitted electrons towards itself and hence the ejected electrons experience retarding force due to development of positive charges on the plate.