A glass plate of refractive index μ₃ is coated with a thin layer of thickness t and refractive index μ₂, where μ₂>μ₃. Light of wavelength λ in air is incident normally on the layer. Choose the correct option(s) for interference of the two reflected waves.
Select all that apply

Question

A glass plate of refractive index μ₃ is coated with a thin layer of thickness t and refractive index μ₂, where μ₂>μ₃. Light of wavelength λ in air is incident normally on the layer. Choose the correct option(s) for interference of the two reflected waves.

Select all that apply

G1 Physics · Accepted Answer

Because μ₂>μ₃ and the wave comes from air, reflection at the air-layer interface has a π phase shift, while reflection at the layer-glass interface has no phase shift. Hence reflected constructive interference occurs for 2μ₂t=(n+1/2)λ and destructive for 2μ₂t=nλ. Therefore A and C are correct.