Von Klitzing constant
ElectromagneticExact
= 25 812.807 45… Ω
- Value
- 25 812.807 45… Ω
- Standard uncertainty
- exact
- Relative uncertainty
- exact
- Status
- Exact since the 2019 SI redefinition
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
NIST prints this exact value cut to 10 digits. ConstantID recomputes it from the defining constants: 25 812.807 459 304 506 660 045 516 7061…
Use in a calculation
# von Klitzing constant, CODATA 2022 (NIST)
R_K = 2.5812807459304506660045516706087443e4 # ohm, exact
# SciPy: scipy.constants.physical_constants['von Klitzing constant']What it is
The quantum of Hall resistance, about 25.8 kΩ. In a thin conducting layer at very low temperature and strong magnetic field, the Hall resistance takes the values R_K/i for whole numbers i, whatever the material. Resistance standards use it, and since 2019 it is exact.
It is built only from constants that have exact values since 20 May 2019, so it is exact too; CODATA 2018 was the first adjustment to list it that way.
Equations
- definition
- quantum Hall plateaus
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). Diamonds mark adjustments in which the value was exact.
Relative uncertainty
| CODATA | Value (uncertainty) | Relative uncertainty | Change from previous |
|---|---|---|---|
| 2022 | 25 812.807 45… | exact | exact |
| 2018 | 25 812.807 45… | exact | −0.9 σ of 2014 |
| 2014 | 25 812.807 4555(59) | 2.3 × 10−10 | +1.4 σ of 2010 |
| 2010 | 25 812.807 4434(84) | 3.3 × 10−10 |
“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).