# Today I Learned

## Qualitative Methods

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

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

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By OctoMiao

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