1. The problem statement, all variables and given/known data I have to do a calculation in electronvolt, using physical constants. The final result must be in electronvolts. I can grab the physical constant from scipy (python library). How do I know which constants I can keep in SI units, and which constants I have to transform? 2. Relevant equations The relevant physical constants are: elementary charge hbar electron mass bohr magneton 3. The attempt at a solution Use the following physical constants: 'elementary charge' (in coulombs) 'Planck constant over 2 pi in eV s' 'electron mass energy equivalent in MeV' * 10^6 / c^2, where c is in m/s 'Bohr magneton in eV/T' I am not sure if I have to scale c, and the elementary charge. Many thanks!