class_docstr: Represents an optical medium for which the permittivity and permeability are known.
  
  This class should never be instantiated directly. Instead it should be
  instantiated indirectly by instantiating Medium with any two of
  permittivity, permeability, and n specified, or by not specifying any
  of permittivity, permeability, or n, in which case default values for
  permittivity and permeability will be used.
  
  Examples
  ========
  >>> from sympy.physics.optics import Medium
  >>> from sympy.abc import epsilon, mu
  >>> m1 = Medium('m1', permittivity=epsilon, permeability=mu)
  >>> m1
  MediumPP(Str('m1'), epsilon, mu)
  >>> m2 = Medium('m2')
  >>> m2
  MediumPP(Str('m2'), 625000*ampere**2*second**4/(22468879468420441*pi*kilogram*meter**3), pi*kilogram*meter/(2500000*ampere**2*second**2))
docstr: Returns magnetic permeability of the medium.
  
  Examples
  ========
  
  >>> from sympy.physics.optics import Medium
  >>> m = Medium('m')
  >>> m.permeability
  pi*kilogram*meter/(2500000*ampere**2*second**2)
docstr_tok: ["Returns","magnetic","permeability","of","the","medium",".","Examples","========",">",">",">","from","sympy.physics.optics","import","Medium",">",">",">","m","=","Medium","(","'m","'",")",">",">",">","m.permeability","pi","*","kilogram","*","meter\/","(","2500000","*","ampere","*","*","2","*","second","*","*","2",")"]
code: def permeability(self):
      """
      Returns magnetic permeability of the medium.
  
      Examples
      ========
  
      >>> from sympy.physics.optics import Medium
      >>> m = Medium('m')
      >>> m.permeability
      pi*kilogram*meter/(2500000*ampere**2*second**2)
  
      """
      return self.args[2]
  
imports: from sympy.physics.units import second, meter, kilogram, ampere
  from sympy.core.basic import Basic
  from sympy.core.symbol import Str
  from sympy.core.sympify import _sympify
  from sympy.functions.elementary.miscellaneous import sqrt
  from sympy.physics.units import speed_of_light, u0, e0
label_desc: Use image node_id 4 for calling the MediumPP obj's underlying member method code with example usage: obj.permeability() and returns: self