# Today I Learned

## Qualitative Methods

In order to do estimations, some relations should be remembered clearly.

- Energy and temperature: \(\frac{1}{40}\mathrm{eV} = 300\mathrm{K} k_B .\)
- Natural units: energy is related to length by \(1\mathrm{fm} = \frac{1}{197\mathrm{MeV}}.\)
- For light, energy \(1\mathrm{eV}\) corresponds to wavelength \(1.24\mathrm{\mu m}\).