Answer
given,
thickness of the oil film = 234 n m
refractive index of oil = n = 1.65
Visible light (in air) has wavelengths between 430 nm (blue) and 770 nm (red)
λ = ?
condition of constructive interference
2 n t + λ/2 = k λ
now,
[tex]\lambda = \dfrac{4nt}{2k - 1}[/tex]
at k = 1
[tex]\lambda = \dfrac{4\times 1.65 \times 234}{2(1) - 1}[/tex]
[tex]\lambda = 1603.8\ nm[/tex]
not between the visible range
at k =2
[tex]\lambda = \dfrac{4\times 1.65 \times 234}{2(2) - 1}[/tex]
[tex]\lambda = 535\ nm[/tex]
above wavelength is in the visible range.
