White Light Is Shone on a Very Thin Layer of Mica

Multiple Choice

White light is shone on a very thin layer of mica ( $\mathrm{n}=1.57)$ , suspended in air, at normal incidence. When the mica layer is observed from the illuminated side, constructive interference is observed for wavelengths of violet $(400 \mathrm{~nm})$ and yellow $(560 \mathrm{~nm})$ light. What is the thickness of the mica layer?

A) $446 \mathrm{~nm}$
B) $892 \mathrm{~nm}$
C) $700 \mathrm{~nm}$
D) $382 \mathrm{~nm}$
E) $764 \mathrm{~nm}$
F) $600 \mathrm{~nm}$