Electrons in hydrogen like atoms (Z = 3) make transitions form the fifth to the fourth orbit and from the fourth to the third orbit. The resulting radiations are incident normally on a metal plate and eject photoelectrons. The stopping potential for the metal and the stopping potential for the photoelectrons ejected by the longer wavelength.

Answer

`2`

Explanation

The stopping potential for shorter wavelength is `3.95` volt i.e., maximum kinetic energy of photoelectrons corresponding to shorter wavelength will be `3.95 eV`. Further energy of incident photons corresponding to shorter wavelength will be in transition from `n=4` to `n=3`
`E_(4-3)=E_(4)-E_(3)=(-(13.6)(3)^(2))/((4)^(2))-[(-(13.6)(3)^(2))/((3)^(2))]=5.95 eV`
Now from the equation,
`K_(max)=E-W`
we have, `W=E-K_(max)=E_(4-3)-K_(max)`
`=(5.95-3.95)eV`
`=2eV`