---
\pagenumbering{gobble}
-<!-- \usepackage{multicols} -->
# Light and Matter
<!--  -->
- $\Delta E = hf = {hc \over \lambda}$ between ground / excited state
-- $E$ and $f$ of photon: $E_2 - E_1 = hf = hc$
+- $E$ and $f$ of photon: $E_2 - E_1 = hf = {hc \over \lambda}$
- Ionisation energy - min $E$ required to remove e-
- EMR is absorbed/emitted when $E_{\operatorname{K-in}}=\Delta E_{\operatorname{shells}}$ (i.e. $\lambda = {hc \over \Delta E_{\operatorname{shells}}}$)