Why would it be impossible to obtain interference fringes in a double-slit experiment if the separation of the slits is less than the wavelength of the light used?

Question

Quizplus · Accepted Answer

The Answer is In no direction could a path difference as large as one wavelength be obtained, and this is needed if a bright fringe, in addition to the central fringe, is to be observed.

Why Would It Be Impossible to Obtain Interference Fringes in a Double-Slit