Answer
Interference due to thin films, also known as thin-film interference, occurs when light reflects off the top and bottom surfaces of a thin film, such as a soap film or oil slick on water. The film must be thin because the interference effect is highly dependent on the difference in the distance traveled by the light reflecting off the top and bottom surfaces of the film.
The reason why we don't see interference effects when looking through a window or at a poster covered by a plate of glass is that the thickness of the glass is much greater than the wavelength of visible light. In a thin film, the thickness is on the order of the wavelength of light, so the difference in the distance traveled by the light reflecting off the top and bottom surfaces of the film is significant and results in interference.
In the case of window or poster covered by a plate of glass, the thickness of the glass is much greater than the wavelength of light and the difference in distance traveled by the light reflecting off the top and bottom surfaces of the glass is much less significant, so interference effects are not observed.
Additionally, the surfaces of the window or poster covered by the plate of glass are not usually parallel to each other, this causes the reflection of light at different angles, and the interference effect would not be observed.
Work Step by Step
Interference due to thin films, also known as thin-film interference, occurs when light reflects off the top and bottom surfaces of a thin film, such as a soap film or oil slick on water. The film must be thin because the interference effect is highly dependent on the difference in the distance traveled by the light reflecting off the top and bottom surfaces of the film.
The reason why we don't see interference effects when looking through a window or at a poster covered by a plate of glass is that the thickness of the glass is much greater than the wavelength of visible light. In a thin film, the thickness is on the order of the wavelength of light, so the difference in the distance traveled by the light reflecting off the top and bottom surfaces of the film is significant and results in interference.
In the case of window or poster covered by a plate of glass, the thickness of the glass is much greater than the wavelength of light and the difference in distance traveled by the light reflecting off the top and bottom surfaces of the glass is much less significant, so interference effects are not observed.
Additionally, the surfaces of the window or poster covered by the plate of glass are not usually parallel to each other, this causes the reflection of light at different angles, and the interference effect would not be observed.
