A non-reflective coating that has a thickness of 198 nm (n = 1.45) is deposited on top of a substrate of glass (n = 1.50). What wavelength of visible light is most strongly transmitted if it is illuminated perpendicular to its surface?

Respuesta :

Answer:

The  wavelength is [tex]\lambda_ 1 = 574.2 nm[/tex]

Explanation:

From the question we are told that  

      The  thickness is [tex]t = 198 nm = 198 *10^{-9 }\ m[/tex]

      The refractive  index of the non-reflective coating is  [tex]n_m = 1.45[/tex]  

       The  refractive  index of glass is [tex]n_g = 1.50[/tex]

       

Generally the condition for  destructive  interference is mathematically represented as

            [tex]2 * n_m * t * cos (\theta) = n * \lambda[/tex]

Where [tex]\thata[/tex] [tex]\theta[/tex] is the angle of refraction which is  0° when the light is strongly transmitted

    and  n is the order maximum interference

        so  

             [tex]\lambda = \frac{2 * n * t * cos (\theta )}{n}[/tex]

at the point n =  1  

           [tex]\lambda _1 = \frac{2 * 1.45 * 198*10^{-9} * cos (0 )}{1}[/tex]

           [tex]\lambda_1 = 574.2 *10^{-9}[/tex]

          [tex]\lambda_1 = 574.2 nm[/tex]

at  n =2  

         [tex]\lambda _2 = \frac{\lambda _1 }{2}[/tex]

         [tex]\lambda _2 = \frac{574.2*10^{-9} }{2}[/tex]

         [tex]\lambda _2 = 2.87 1 *10^{-9} \ m[/tex]

         [tex]\lambda _2 = 287. 1 nm[/tex]

Now we know that the wavelength range of visible light is  between

           [tex]390 \ nm \to 700 \ nm[/tex]

   So the wavelength of visible light that is been transmitted is  

          [tex]\lambda_ 1 = 574.2 nm[/tex]