'**************************************************************
'*  Calculate angle of refraction for an incident ray using   *
'*  Snell's Law                                               *
'* ---------------------------------------------------------- *
'* SAMPLE RUN:                                                *
'*                                                            *
'* Give indices for incident and refracting medium: 1, 1.5    *
'*                                                            *
'* What is the angle of incidence? 30                         *
'*                                                            *
'* Refracted angle =  19.4712                                 *
'*                                                            *
'* ---------------------------------------------------------- *
'* Ref.: "Problem Solving with Fortran 90 By David R. Brooks, *
'*        Springer-Verlag New York, 1997".                    *
'*                                                            *
'*                        Basic Release By J-P Moreau, Paris. *
'*                                 (www.jpmoreau.fr)          *
'**************************************************************
' Explanations:
' ------------               \ i!
'                    incident \ !
'                      beam    \!
'                   ---------------------------
'                               !*
'                               ! *  refracted
'                               !r *   beam
'
'
'               Snell's Law:  n sin(i) = n sin(r)
'                              i          r
'                           -1
'               or   r = sin  [(n / n ) sin(i)]
'                                i   r
'
'--------------------------------------------------------------
'Program Refract
DEFDBL A-H, O-Z


' xni, xnr: double;           (indices of refraction (dimensionless) )
' xincident,refracted:double; (angles from perpendicular (deg) )
' DegToRad: double;           (required for trig functions )
' sinus,cosinus: double;      (auxiliary trig values )

  pi = 3.1415926535#

  DegToRad = pi / 180#

  CLS
  PRINT
  INPUT " Give indices for incident and refracting medium: ", xni, xnr

  PRINT
  INPUT " What is the angle of incidence? ", xincident

' Convert refracted angle to degrees before displaying its value

  sinus = xni / xnr * SIN(xincident * DegToRad)

  cosinus = SQR(1# - sinus * sinus)

  refracted = ATN(sinus / cosinus)

  F$ = "###.####"

  PRINT
  PRINT " Refracted angle = ";
  PRINT USING F$; refracted / DegToRad

END

'end of file refract.bas