What wavelength monochromatic source in the visible region (390 to 710 nm)can be used to constructively reflect off a soap film (n = 1.46)if the film is 240 nm thick?
A)467 nm
B)562 nm
C)587 nm
D)480 nm

Question

Quizplus · Accepted Answer

Constructive interference occurs when the path length difference between two waves is an integer multiple of the wavelength. In this case, the path length difference is twice the thickness of the soap film, or 480 nm. Therefore, the wavelength of the monochromatic source must be 480 nm / 2 = 240 nm. The only choice that is close to this value is 467 nm.

What Wavelength Monochromatic Source in the Visible Region (390 to 710