Notation of physical constants

11.2.1 Notation of physical constants

If you want to use a physical constants inside Xcas, put its name between two characters _ ("underscore"). Don’t 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 11.3 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/charge of the electron)

_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_ Constante universelle des gaz _me_ Electron rest mass

_Rinfinity_ Rydberg constant _mp_ Proton rest mass

_StdP_ Standard pressure _mpme_ Quotient mp/me (mass of the proton/mass of the electron)

_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*epsilon0 (charge of the electron*permittivity)

_epsilon0_ Permittivity of vacuum _qme_ Quotient q/me (charge/mass of the electron)

_epsilon0q_ epsilon0/q (permittivity/charge of the electron) _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_ 2π

Table 11.3: Physical constants

Examples.

Input:
_c_
Output:
1 c

which represents the speed of light in vacuum. You can use the mksa command (see Section 11.1.3) to put this in terms of standard units:
Input:
mksa(_c_)
Output:
299792458.0 m s⁻¹
Input:
_NA_
Output:
1 N_A

which represents Avogadro’s number:
Input:
mksa(_NA_)
Output:
6.0221367×10²³ mol⁻¹

_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/charge of the electron)
_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_	Constante universelle des gaz	_me_	Electron rest mass
_Rinfinity_	Rydberg constant	_mp_	Proton rest mass
_StdP_	Standard pressure	_mpme_	Quotient mp/me (mass of the proton/mass of the electron)
_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_	qepsilon0 (charge of the electronpermittivity)
_epsilon0_	Permittivity of vacuum	_qme_	Quotient q/me (charge/mass of the electron)
_epsilon0q_	epsilon0/q (permittivity/charge of the electron)	_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_	2π