### 5.2.2 Constants Library

The physical constants are in the `Phys` menu, `Constant` sub-menu. The following table gives the Constants Library :

Name | Description
`_NA_` | Avogadro’s number
`_k_` | Boltzmann constant
`_Vm_` | Molar volume
`_R_` | Universal gas constant
`_StdT_` | Standard temperature
`_StdP_` | Standard pressure
`_sigma_` | Stefan-Boltzmann constant
`_c_` | Speed of light in vacuum
`_epsilon0_` | Permittivity of vacuum
`_mu0_` | Permeability of vacuum
`_g_` | Acceleration of gravity
`_G_` | Gravitational constant
`_h_` | Planck’s constant
`_hbar_` | Dirac’s constant
`_q_` | Electron charge
`_me_` | Electron rest mass
`_qme_` | q/me (Electron charge/masse)
`_mp_` | Proton rest mass
`_mpme_` | mp/me (proton masse/electron masse)
`_alpha_` | Fine structure constant
`_phi_` | Magnetic flux quantum
`_F_` | Faraday constant
`_Rinfinity_` | Rydberg constant
`_a0_` | Bohr radius
`_muB_` | Bohr magneton
`_muN_` | Nuclear magneton
`_lambda0_` | Photon wavelength (ch/e)
`_f0_` | Photon frequency (e/h)
`_lambdac_` | Compton wavelength
`_rad_` | 1 radian
`_twopi_` | 2*pi radians
`_angl_` | 180 degrees angle
`_c3_` | Wien displacement constant
`_kq_` | k/q (Boltzmann/electron charge)
`_epsilon0q_` | epsilon0/q (permitivity /electron charge)
`_qepsilon0_` | q*epsilon0 (electron charge *permitivity)
`_epsilonsi_` | Silicium dielectric constant
`_epsilonox_` | Bioxyd of silicium dielectric constant
`_I0_` | Reference intensity

To have the value of a constant, input the constant name in the command line of `Xcas` and valid with `enter` (don’t forget to put `_` at the begining and at the end of the constant name).