Chapter 27 - Early Quantum Theory and Models of the Atom - Problems - Page 799: 29

$E=\frac{1240\;eV \cdot nm }{\lambda (in\;nm)}$

Use equation 27–4, E = hf, and recall that $\lambda f = c$. $$E=hf=\frac{hc}{\lambda}$$ Insert values and convert units. $$E=\frac{(6.626\times10^{-34}J \cdot s)(2.998\times10^8m/s)}{\lambda}\frac{eV/1.602\times10^{-19}J}{(10^{-9}m/nm)}$$ $$E=\frac{1240\;eV \cdot nm }{\lambda (in\;nm)}$$