# Constants

The Constants element contains a set of pre-defined physical constants that can be used in other elements of the simulation. Constants are just a number. You may add new constants by clicking the Add button under the Elements Tree while the Constants element (in the Elements Tree) is highlighted. For information on the Elements Tree, see the images in the RSim User Guide: Setup Window for Simulations page.

kind (not editable) The kind of constant; either a built-in kind or a User Defined kind.

description (only for User Defined constants) A descriptive name of the constant.

value The value of the constant. This is the user-supplied value of the constant if kind = User Defined. Otherwise it is a non-editable value supplied by RSim.

## Built-In Constants:

• PI: The ratio of the circumference of a circle to its diameter.
• 3.141592653589793
• PIO2: $$\pi$$ divided by two.
• 1.5707963267948966
• TWOPI: $$\pi$$ multiplied by two.
• 6.283185307179586
• LIGHTSPEED: The speed of light in vacuum (in meters/second).
• 299792458.0
• MU0: The permeability of free space (in newtons/amp^2 or (tesla meters)/amp) .
• 1.2566370614359173e-06
• ELEMCHARGE: The fundamental unit of charge (in coulombs).
• 1.602176487e-19
• ELECMASS: The mass of an electron (in kilograms).
• 9.10938215e-31
• PROTMASS: The mass of a proton (in kilograms).
• 1.672621637e-27
• MUONMASS: The mass of a muon (in kilograms).
• 1.8835313e-28
• KB: Boltzmann’s constant in (joules/kelvin)
• 1.3806504e-23
• EPSILON0: The permittivity of free space (in farads/meters or (amps^2 seconds^4)/(meters^3 kilograms)).
• 8.854187817620389e-12
• C2: The speed of light squared (in meters^2/seconds^2).
• 8.987551787368176e+16
• ELECCHARGE: The charge of an electron (in coulombs).
• (-1.602176487e-19)
• ELECMASSEV: The mass of an electron (in eV/c^2).
• 510998.90984764055