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 214 nm thick?
A)417 nm
B)446 nm
C)406 nm
D)489 nm
E)479 nm

Question

Quizplus · Accepted Answer

The condition for constructive interference in a soap film is given by the equation:

2nt = mλ

where n is the refractive index of the soap film, t is the thickness of the film, m is the order of the interference, and λ is the wavelength of the incident light.

We want to find the wavelength of a monochromatic source that will cause constructive interference for the first-order (m=1) reflection off the soap film.

Plugging in the given values, we get:

2(1.46)(214 x 10^-9 m) = (1)λ

λ = 417 nm

Therefore, the best choice is A) 417 nm.

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