What is the minimum thickness of a soap bubble film with refractive index 1.38 that results in a constructive interference in the reflected light if this film is illuminated by a beam of light of
Wavelength 610 nm?
A) 444 nm
B) 222 nm
C) 555 nm
D) 333 nm
E) 111 nm

Question

Quizplus · Accepted Answer

For constructive interference in a thin film, the minimum thickness (t) is given by t = (mλ)/(2n), where m is an integer (for minimum thickness, m=1), λ is the wavelength of light, and n is the refractive index. Substituting the values, t = (1 * 610 nm) / (2 * 1.38) = 221.74 nm, which rounds to 222 nm. However, due to the phase change upon reflection, the effective path difference is half the wavelength, leading to the minimum thickness being half of 222 nm, which is approximately 111 nm.

What Is the Minimum Thickness of a Soap Bubble Film