The formula is simple.
Kinetic energy = Photon energy - Binding energy
In some places, binding energy is also called work function.
So, Photon energy = [tex] \frac{hc}{\lambda} [/tex]
= [tex] \frac{6.6 \times 10^{-34} \times 3 \times 10^8}{1.57 \times 10^2 \times 10^{-9}} [/tex] (Here we multiply lambda by 10^(-9) to change nm to m)
= [tex]1.261 \times 10^{-18}[/tex] J
Change it to ev from Joule (J)
so, Photon energy = [tex]1.261 \times 10^{-18}[/tex] J = [tex] \frac{1.261 \times 10^{-18}}
{1.6 \times 10^{-19}} [/tex]
= 7.8 eV
Now, KE = 7.8 - 3.31 = 4.57 eV
Done !!!
