Answer:
[tex]343.31\times 10^{-9}m[/tex]
Explanation:
For constructive interference, condition is that ( m=0,1,2.....)
[tex]2nt=(m+\frac{1}{2})\lambda[/tex]
Take for m=1,
[tex]2nt=(\frac{3}{2})\lambda[/tex]
Given that, the refractive index of a thin film is,
[tex]n=1.42[/tex]
And the wavelength of the light is,
[tex]\lambda=650 nm=650\times 10^{-9}m[/tex]
Now,
[tex]2t=\frac{3}{2}\frac{ (650\times 10^{-9})}{1.42} \\t=\frac{3}{4}\frac{ (650\times 10^{-9})}{1.42}\\t=343.31\times 10^{-9}m[/tex]
Therefore, the thickness of film which create reflected light is [tex]343.31\times 10^{-9}m[/tex]
