A thin film of oil strongly reflects blue light. Should the oil be made thicker or thinner to reflect red light?
Which is the shorter wavelength ?
the blue light is the shorter wavelength. What does that mean in regards to this?
Think about it or google oil slick reflection wavelengths and look at the geometry in the images. You will see that the shorter the wavelength the thinner the film.
Thank you!
To understand whether the thickness of the oil film needs to be increased or decreased to reflect red light instead of blue light, we need to consider the process of thin film interference and the concept of optical path difference.
When light waves strike an interface between two media with different refractive indices, such as air and oil, some of the light is reflected while the rest is transmitted and refracted. In the case of a thin film of oil, both reflections from the upper and lower surfaces of the film occur. These reflected waves can interfere constructively or destructively depending on the wavelength and the optical path difference.
In the case of blue light, which has a shorter wavelength than red light, a thin film of oil of a certain thickness can create constructive interference for blue light waves. This happens when the optical path difference between the two reflections is equal to an integer multiple of the blue light's wavelength. As a result, the blue light is reflected, creating a blue appearance.
To understand how the reflection of red light is achieved, we need to consider the relationship between optical path difference and wavelength. Since red light has a longer wavelength than blue light, it requires a greater optical path difference to create constructive interference.
Therefore, to reflect red light instead of blue light, we need to increase the thickness of the oil film. By increasing the thickness, we increase the optical path difference between the two reflections, allowing for constructive interference of red light waves. Consequently, the oil film will appear red when it reflects light.
In summary, to shift the reflection color from blue to red, the oil film needs to be made thicker.