SI Defining Constants
Q
What are SI Defining Constants?
✍: FYIcenter.com
A
SI specifies 7 constants, which are used to define
measurements of 7 base units. See the table below.
| Symbol | Exact Quantity | Defining Constant | Defining Unit |
| ΔνCs | hyperfine transition frequency of 133Cs | 9192631770 s-1 | s for time |
| c | speed of light | 299792458 m⋅s-1 | m for length |
| h | Planck constant | 6.62607015×10−34 kg⋅m2⋅s-1 | kg for mass |
| e | elementary charge | 1.602176634×10−19 A⋅s | A for electric current |
| k | Boltzmann constant | 1.380649×10−23 kg⋅m2⋅s-2⋅K-1 | K for thermodynamic temperature |
| NA | Avogadro constant | 6.02214076×1023 mol−1 | mol for amount of substance |
| Kcd | luminous efficacy of 540 THz radiation | 683 cd⋅kg−1⋅m−2⋅s3 | cd for luminous intensity |
⇒ Names and Symbols of SI Unites
⇐ International System of Units (SI)
2026-10-28, ∼1933🔥, 0💬
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