For a coherent plane wave approaching an obstacle with a rectangular opening, diffraction becomes significant under which of the following circumstances?
A) both dimensions of the rectangular opening are comparable to the wavelength
B) one or more dimensions of the rectangular opening are comparable to the wavelength
C) both dimensions of the rectangular opening are larger than the wavelength
D) only if the opening is circular

Question

Quizplus · Accepted Answer

Diffraction becomes significant when one or more dimensions of the obstacle (in this case, the rectangular opening) are comparable to the wavelength of the approaching wave. Therefore, option B is the correct choice. Option A is incorrect because both dimensions being comparable to the wavelength would make the obstacle a so-called "diffraction grating," which exhibits more complex diffraction patterns than a simple rectangular opening. Option C is incorrect because when the dimensions of the obstacle are much larger than the wavelength, diffraction is negligible and the wave mostly passes straight through. Option D is incorrect because circular openings also exhibit significant diffraction, but the prompt asks specifically about rectangular openings.

For a Coherent Plane Wave Approaching an Obstacle with a Rectangular