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+//Chapter-1,Example 1_20_1,Page 1-52
+clc()
+
+//Given Data:
+i=45*%pi/180         //angle of incidence
+u=1.2                //Refractive index of a film
+t=4*10^-7            //thickness of film
+
+//Calculations:
+//u=sin i/sin r      //Snell's law   .So,
+r=asin(sin(i)/u)     //angle of reflection
+
+//Now, condition for dark fringe is
+//2ut*cos r=n*lam
+lam1=2*u*t*cos(r)/1          //n=1
+printf('For n=1 wavelength is =%.10f m \n',lam1)
+printf(' This is in the visible spectrum and it will remain absent.\n \n') 
+
+lam2=2*u*t*cos(r)/2          //n=2
+printf(' For n=2 wavelength is =%.10f m \n',lam2)
+printf(' This is not in the visible spectrum \n \n')