The work function is
e W 0 = h ν t h = h c λ = 12400 eV ⋅ Å 6000 Å = 2.07 eV {\displaystyle eW_{0}=h\nu _{th}={\frac {hc}{\lambda }}={\frac {12400{\text{ eV}}\cdot \mathrm {\AA} }{6000\,\mathrm {\AA} }}=2.07{\text{ eV}}}
The photoelectric equation then gives
e V s = h ν − e W 0 = h c λ − e W 0 {\displaystyle eV_{s}=h\nu -eW_{0}={\frac {hc}{\lambda }}-eW_{0}}
2.5 eV = 12400 eV ⋅ Å λ − 2.07 eV ⇒ λ = 2713 Å {\displaystyle 2.5{\text{ eV}}={\frac {12400{\text{ eV}}\cdot \mathrm {\AA} }{\lambda }}-2.07{\text{ eV}}\Rightarrow \lambda =2713\,\mathrm {\AA} }
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