!**************************************************************
!*  Calculate angle of refraction for an incident ray using   *
!*  Snell's Law                                               *
!* ---------------------------------------------------------- *
!* SAMPLE RUN:                                                *
!*                                                            *
!* Give indices for incident and refracting medium: 1.0 1.5   *
!*                                                            *
!* What is the angle of incidence? 30                         *
!*                                                            *
!* Refracted angle =   19.47122                               *
!*                                                            *
!* ---------------------------------------------------------- *
!* Ref.: "Problem Solving with Fortran 90 By David R. Brooks, *
!*        Springer-Verlag New York, 1997".                    * 
!**************************************************************
! 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
  Implicit None
  Real ni, nr             !indices of refraction (dimensionless)
  Real incident,refracted !angles from perpendicular (deg)
  Real DegToRad           !required for trig functions

  Real, parameter :: pi = 3.1415926537

  DegToRad = pi/180.

  print *,' '
  write(*,10,advance='no'); read *, ni, nr

  print *,' '
  write(*,20,advance='no'); read *, incident

! Convert refracted angle to degrees before displaying its value

  refracted = ASIN(ni/nr*SIN(incident*DegToRad))

  print *,' '
  print *,'Refracted angle = ', refracted/DegToRad
  print *,' '

  stop

10 format(' Give indices for incident and refracting medium: ')
20 format(' What is the angle of incidence? ')

End

!end of file refract.f90