import math
##Example 8.2
##Polarizer,calculation of angle
##given values
Io=1.;##intensity of polarised light
I1=Io/2.;##intensity of beam polarised by first by first polariser
I2=Io/3.;##intensity of light polarised by second polariser
##calculation
a=math.acos(math.sqrt(I2/I1));
alpha=a*180./math.pi;##conversion of angle into degree
print'%s %.1f %s'%('angle between characteristic directions (in degree) is',alpha,'');
import math
##Example 8.3
##calculation of birefringence
##given values
l=6*10**-7.;##wavelength of light in metre
d=3*10**-5.;##thickness of crystal
##calculation
x=l/(4.*d);
print'%s %.3f %s'%('the birefringance of the crystal is',x,'');