Answer:
184 nm
Explanation:
Given that ;
the refractive index (n) of ethyl alcohol = 1.36
wavelength ([tex]\lambda[/tex]) = 500 nm = 500 × 10⁻⁹ m
The difference in optical path length between the adjacent light rays can be expressed by the formula:
[tex]\lambda = 2n_fdcos \theta_f[/tex]
where;
[tex]\theta_f[/tex] = relative phase difference
d = distance between points of reflections
[tex]n_f[/tex] = refractive index of the film
If we replace [tex]m \lambda_f[/tex] for [tex]\lambda[/tex] in the above equation; we have;
[tex]m \lambda_f = 2n_fdcos \theta[/tex]
where; m represents the order of the pattern of the light rays;
and θ = 0; m = 1
Making d the subject of the formula; we have:
[tex]d = \frac{m \lambda_f}{2n_fcos \theta_f}[/tex]
[tex]d = \frac{1* 500 nm}{2*(1.36)cos(0)}[/tex]
d = 184 nm
∴ The thickness of the film = 184 nm
