![]() The candela, symbol cd, is the SI unit of luminous intensity in a given direction. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles. The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. This number is the fixed numerical value of the Avogadro constant, N A, when expressed in the unit mol -1 and is called the Avogadro number. One mole contains exactly 6.022 140 76 x 10 23 elementary entities. The mole, symbol mol, is the SI unit of amount of substance. It is defined by taking the fixed numerical value of the Boltzmann constant k to be 1.380 649 x 10 -23 when expressed in the unit J K -1, which is equal to kg m 2 s -2 K -1, where the kilogram, meter and second are defined in terms of h, c and Δ ν Cs. The kelvin, symbol K, is the SI unit of thermodynamic temperature. It is defined by taking the fixed numerical value of the elementary charge e to be 1.602 176 634 x 10 -19 when expressed in the unit C, which is equal to A s, where the second is defined in terms of Δ ν Cs. The ampere, symbol A, is the SI unit of electric current. It is defined by taking the fixed numerical value of the cesium frequency Δ ν Cs, the unperturbed ground-state hyperfine transition frequency of the cesium 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s -1. The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10 -34 when expressed in the unit J s, which is equal to kg m 2 s -1, where the meter and the second are defined in terms of The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the speed of light in vacuum c to be 299 792 458 when expressed in the unit m s -1, where the second is defined in terms of ![]() The meter, symbol m, is the SI unit of length. The following seven SI base unit definitions are based on the BIPM SI Brochure (9th Edition). Become familiar with the seven defining constants of the SI.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |