24.2.1 Notation of physical constants
If you want to use a physical constants inside Xcas, put its name
between two characters _ (“underscore”).
Do not confuse physical constants with symbolic constants; for example,
e,π are symbolic constants and _c_,_NA_ are physical
constants. The physical constants are in the Phys menu,
Constant sub-menu, and table
24.3 gives the Constants Library:
| _F_ | Faraday constant | _h_ | Planck’s constant |
| _G_ | Gravitational constant | _hbar_ | Dirac’s constant |
| _I0_ | Reference intensity | _k_ | Boltzmann constant. |
| _NA_ | Avogadro’s number | _kq_ | k/q (Boltzmann/electron charge) |
| _PSun_ | Power at the surface of the Sun | _lambda0_ | Photon wavelength (ch/e) |
| _REarth_ | Radius of the Earth | _lambdac_ | Compton wavelength |
| _RSun_ | Radius of the Sun | _mEarth_ | Mass of the Earth |
| _R_ | Universal gas constant | _me_ | Electron rest mass |
| _Rinfinity_ | Rydberg constant | _mp_ | Proton rest mass |
| _StdP_ | Standard pressure | _mpme_ | Quotient mp/me (proton mass/electron mass) |
| _StdT_ | Standard temperature | _mu0_ | Permeability of vacuum |
| _Vm_ | Molar volume | _muB_ | Bohr magneton |
| _a0_ | Bohr radius | _muN_ | Nuclear magneton |
| _alpha_ | Fine structure constant | _phi_ | Magnetic flux quantum |
| _angl_ | 180 degree angle | _q_ | Charge of an electron |
| _c3_ | Wien displacement constant | _qe_ | Electron charge |
| _c_ | Speed of light in vacuum | _qepsilon0_ | q· ε0 (electron charge*permittivity) |
| _epsilon0_ | Permittivity of vacuum | _qme_ | Quotient q/me (charge/electron mass) |
| _epsilon0q_ | ε0/q (permittivity/electron charge) | _rad_ | 1 radian |
| _epsilonox_ | Dielectric constant of Silicon dioxide | _sd_ | Duration of a sidereal day |
| _epsilonsi_ | Dielectric constant | _sigma_ | Stefan-Boltzmann constant |
| _f0_ | Photon frequency (e/h) | _syr_ | Duration of a sidereal year |
| _g_ | Acceleration of gravity | _twopi_ | 2 π |
| Table 24.3: Physical constants in Xcas |
Example
To get the object representing the speed of light in vacuum, enter:
Use the mksa command (see Section 24.1.3)
to put this in terms of standard units: