Monochromatic light, at normal incidence, strikes a thin film in air.If $\lambda$ denotes the wavelength in the film, what is the thinnest film in which the reflected light will be a maximum?
A)"much less than $\lambda$"
B)"$\lambda$/4"
C)"$\lambda$/2"
D)"3$\lambda$/4"
E)"$\lambda$"

Question

Quizplus · Accepted Answer

The thinnest film that will result in maximum reflection is when the reflected waves from the top and bottom surfaces of the film interfere constructively. This occurs when the path difference between the two reflected waves is equal to an integer multiple of the wavelength in the film. As the angle of incidence is normal, the path difference is equal to twice the thickness of the film, and we want this to be equal to an integer multiple of the wavelength in the film. Therefore, the thinnest film for maximum reflection will have a thickness of λ/4 in the film (since we want the path difference to be λ/2).
Thus, the answer is B: F1F1F1S1λF1F1F10/4.

Monochromatic Light, at Normal Incidence, Strikes a Thin Film in Air.If