Question

ASK YOUR TEACHER An oil slick on water is 99.8 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, in nanometers), given its index of refraction is 1.38

Answer 1

There will be a phase change at the 1-1.38 interface and no phase change at the 1.38-1.33 interface.

At a thickness of lambda / 4 (y/4) one should get constructive interference for the reflected light.

y = 4 * 99.8 * 10E-9 m = 400 nm (about) = 4 * 10E-7 m

The color of this light will be violet or blue