A thin film of oil of refractive index 1.5 and thickness 600 nm is floating on water of refractive index 1.33 . White light is incident normally on the film. Which of the following is the longest wavelength in the visible spectrum ( 400 nm

Question

A thin film of oil of refractive index 1.5 and thickness 600 nm is floating on water of refractive index 1.33 . White light is incident normally on the film. Which of the following is the longest wavelength in the visible spectrum ( 400 nm to 700 nm ) that is maximally transmitted?

Quantrex Academy · Accepted Answer

Correct answer: C. 600 nm

When light reflects from the air-oil interface (refractive index 1.0 to 1.5 ), it undergoes a phase change of . When light reflects from the oil-water interface (refractive index 1.5 to 1.33 ), it reflects from a rarer medium, so there is no phase change. The relative phase shift between the two reflected waves is . For maximum transmission, the reflected light must undergo destructive interference (minimum intensity). The condition for destructive interference in reflected light with a relative phase shift of is:

A thin film of oil of refractive index 1.5 and thickness 600 nm is floating on water of refractive index 1.33 . White light is incident normally on the film. Which of the following is the longest wavelength in the visible spectrum ( 400 nm to 700 nm ) that is maximally transmitted?

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