Question

An oil slick on water is 120 nm thick and illuminated by white light incident perpendicular to its surface. What color does the oil appear (what is the most constructively reflected wavelength), given its index of refraction is 1.40?

Answer 1

Answer:

$\lambda = 672 nm$

so this is nearly red colour light

Explanation:

As we know that the interference of light from reflected light then the path difference is given as

$\Delta x = 2\mu t + \frac{\lambda}{2}$

now we know that for constructive interference of light the path difference is given as

$\Delta x = n\lambda$

so we will have

$2\mu t + \frac{\lambda}{2} = N\lambda$

so we will have

$4\mu t = \lambda$

$\lambda = 2(1.40)(120nm)$

$\lambda = 672 nm$

so this is nearly red colour light