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## Homework Statement

A sodium atom emits a photon with wavelength 818 nm shortly after being struck by an electron. What minimum speed did the electron have before the collision?

## Homework Equations

[itex]E_{particle}\geq\Delta E_{atom}[/itex]

## The Attempt at a Solution

For the minimum energy, [itex]E_{particle}=\Delta E_{atom}[/itex], and because the photon was emitted due to the collision:

[itex]\frac{m_ev^2}{2}=\frac{hc}{\lambda}[/itex]

[itex]m_ev^2=\frac{2hc}{\lambda}[/itex]

[itex]v=\sqrt{\frac{2hc}{m_e \lambda}}[/itex]

[itex]v=\sqrt{\frac{2 \times 1239.842 \mathrm{eV} \times \mathrm{nm}}{9.11 \times 10^{-31} \times 818 \mathrm{nm} \times \mathrm{kg}}}[/itex]

When I evaluate this, I get [itex].73 \times 10^6 \frac{\mathrm m}{\mathrm s}[/itex], which Mastering Physics tells me is wrong. Is there something obvious I'm missing here?