When two pieces of glass are pressed together in air and illuminated with coherent light, the place where they are in contact will look
A) dark.
B) bright.
C) Hold it! Its appearance will oscillate between dark and bright.
D) Hold it! Though the appearance will be steady in time, more information is needed to answer this question unambiguously.

Question

Quizplus · Accepted Answer

When two pieces of glass are pressed together in air and illuminated with coherent light, the place where they are in contact will look dark due to the principle of destructive interference of light waves at the point of contact where the path difference is minimal.

When Two Pieces of Glass Are Pressed Together in Air