Electron charge to mass quotient

$− e/mₑ$ = −1.758 820 008 38(55) × 10¹¹ C kg⁻¹

Value: −1.758 820 008 38 × 10¹¹ C kg⁻¹
Standard uncertainty: 55 C kg⁻¹
Relative uncertainty: 3.1 × 10⁻¹⁰ (313 parts per trillion)
Status: Measured
Symbol: $− e/mₑ$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# electron charge to mass quotient, CODATA 2022 (NIST)
electron_charge_to_mass_quotient = -1.75882000838e11  # C kg^-1, standard uncertainty 55

# SciPy: scipy.constants.physical_constants['electron charge to mass quotient']

What it is

The electron's charge divided by its mass, −e/mₑ. J. J. Thomson measured this ratio in 1897 when he identified the electron; it sets how strongly electric and magnetic fields bend an electron beam.

How the value changed, 1998–2022

Each point is one CODATA adjustment, plotted as its difference from the 2022 value; the bars show one standard uncertainty (an arrowhead means the bar runs off the chart).

Relative uncertainty

CODATA	Value (uncertainty)	Relative uncertainty	Change from previous
2022	−1.758 820 008 38(55) × 10¹¹	3.1 × 10⁻¹⁰	+4.5 σ of 2018
2018	−1.758 820 010 76(53) × 10¹¹	3.0 × 10⁻¹⁰	+1.2 σ of 2014
2014	−1.758 820 024(11) × 10¹¹	6.3 × 10⁻⁹	+1.6 σ of 2010
2010	−1.758 820 088(39) × 10¹¹	2.2 × 10⁻⁸	+1.4 σ of 2006
2006	−1.758 820 150(44) × 10¹¹	2.5 × 10⁻⁸	−0.2 σ of 2002
2002	−1.758 820 12(15) × 10¹¹	8.5 × 10⁻⁸	+0.8 σ of 1998
1998	−1.758 820 174(71) × 10¹¹	4.0 × 10⁻⁸

“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).