!********************************************************
!* Calculate relativistic mass and speed of an electron *
!* accelerated in an electron gun                       *
!* ---------------------------------------------------- *
!* SAMPLE RUN:                                          *
!*                                                      *
!* Give electron gun voltage in volts: 1e6              *
!*                                                      *
!* Relativistic mass (kg) and speed (m/s):              *
!*  2.6933944E-30  2.8212490E+08                        *
!*                                                      *
!* ---------------------------------------------------- *
!* Ref.: "Problem Solving with Fortran 90 By David R.   *  
!*        Brooks, Springer-Verlag New York, 1997".      *  
!********************************************************
!Explanations:
!------------
!
! An electron accelerated by a voltage V in an electron gun
!
!                              2     2
! acquires an energy of Ve = mc - m c,  where
!                                  0
!                                        -19
!  charge on an electron   e = 1.602 x 10    coulomb
!
!                                         -31
!  rest mass               m  = 9.109 x 10    kg
!                           0
!                                         8 
!  speed of light          c = 2.9979 x 10  m/s
!
! The speed v of an electron of relativistic mass m (kg) is
! obtained from
!                                          2
!                 m/m  = 1 / sqrt(1 - (v/c) )
!                    0
!
!-----------------------------------------------------------
Program Rel_Mass

  Implicit None    !All variables must be declared

  Real rest_mass, rela_mass    ! kg
  Real voltage                 ! volt
  Real speed                   ! m/s
  Real e                       ! electron charge in coulomb
  Real c                       ! speed of light in m/s

  Parameter (e=1.602e-19, c=2.9979e8, rest_mass=9.109e-31)

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

  rela_mass = (voltage*e + rest_mass*c**2) / c**2

  speed = c*(1. - (rest_mass/rela_mass)**2)**0.5

  print *,' '
  print *,'Relativistic mass (kg) and speed (m/s):'
  print *, rela_mass, speed

  print *,' '

10 format(' Give electron gun voltage in volts: ')

End

!End of file rel_mass.f90