# Chapter 9 Interference¶

## Example 9.1 Page no 136¶

In :
#given
t=0.2                                     #Thickness of film in micro m
r=1.25                                    #Refractive index of liquid
w=(4000,5000)                             #Range of wavelength in Angstrom
q=35                                      #Angle observed in degrees

#Calculations
import math
u=math.asin(math.sin(q*3.14/180.0)/r)*180/3.14
w1=(2*t*10**-6*r*math.cos(u*3.14/180.0))/10**-10
w2=w1/2.0

#Output
print"Wavelength absent in reflected light is ",round(w2,0),"Angstrom"

Wavelength absent in reflected light is  2222.0 Angstrom


## Example 9.2 Page no 136¶

In :
#given
r=1.39                                                #Refractive index of the film
q=30                                                  #Angle observed in degrees
w=(5125,5000)                                         #Wavelengths of two consecutive dark bands in Angstrom

#Calculations
import math
r1=math.asin(math.sin(q*3.14/180.0)/r)*180/3.14
n=w/(w-w)
t=((n*w*10**-8)/(2.0*r*math.cos(r1*3.14/180.0)))/10**-4

#Output
print"Thickness of the film is ",round(t,4),"*10**-4 cm"

Thickness of the film is  7.9026 *10**-4 cm


## Example 9.3 Page no 137¶

In :
#given
r=1.4                                            #Refractive index of the material
w=5893                                           #Wavelength of yellow light in Angstrom
n=10                                             #Number of bands
w1=0.009                                         #Width of band in m

#Calculations
import math
b=math.asin((w*10**-8)*180/3.14/(2.0*r*n*w1))

#Output
print"Angle of wedge is ",round(b,4),"degrees"

Angle of wedge is  0.0134 degrees


## Example 9.4 Page no 137¶

In :
#given
r=1.0                                              #Refractive index
n=4                                                #Number of bands
w=6500                                             #Wavelength in Angstrom

#Calculations
t=(((n+(1/2.0))*w*10**-8)/(2*r))/10.0**-4

#Output
print"Thickness of wedge shaped air film is ",t,"*10**-4 cm"

Thickness of wedge shaped air film is  1.4625 *10**-4 cm


## Example 9.5 Page no 137¶

In :
#given
d=0.5                                          #Diameter of the ring in cm
n=4                                            #number of bands
w=5893                                         #Wavelength of light in Angstrom
q=30                                           #Angle at which light enters in degrees

#Calculations
import math
R=((d**2*math.cos(q*3.14/180.0))/(2.0*(2*n+1)*w*10**-8))

#Output
print"Radius of curvature of lens is ",round(R,1),"cm"

Radius of curvature of lens is  204.1 cm