Thin films: A 360-nm thick oil film floats on the surface of the water. The indices of refraction of the oil and the water are 1.5 and 1.33, respectively. The surface of the oil is illuminated from above at normal incidence with white light. What TWO wavelengths of light in the 400-nm to 800-nm wavelength band are most strongly reflected?

Question

Quizplus · Accepted Answer

The condition for constructive interference in a thin film is $2nt = m\lambda$, where $n$ is the refractive index of the film, $t$ is the thickness, and $\lambda$ is the wavelength. For the oil film, $2 \times 1.5 \times 360 \, \text{nm} = m\lambda$. Solving for $\lambda$ gives wavelengths around 430 nm and 720 nm within the given range.

Thin Films: a 360-Nm Thick Oil Film Floats on the Surface