Two parallel glass plates of index of refraction n are separated by an air film of thickness d. Light of wavelength $\lambda$ in air, normally incident on the plates, is intensified on reflection when, for some integer m
A) 2d = m$\lambda$
B) 2d = m$\lambda$0/n
C) 2d = mn$\lambda$
D) 2d = (m + 1/2)$\lambda$
E) 2nd = m$\lambda$ /2

Question

Two parallel glass plates of index of refraction n are separated by an air film of thickness d. Light of wavelength $\lambda$ in air, normally incident on the plates, is intensified on reflection when, for some integer m
A) 2d = m$\lambda$ 
B) 2d = m$\lambda$0/n 
C) 2d = mn$\lambda$ 
D) 2d = (m + 1/2)$\lambda$ 
E) 2nd = m$\lambda$ /2

Quizplus · Accepted Answer

The condition for constructive interference for light waves reflected from parallel glass plates is given by: 
2d = (m + 1/2)λ/n 
where d is the thickness of the air film, λ is the wavelength of the incident light in air, n is the refractive index of the glass, and m is an integer representing the order of the interference.

Since the question asks for the condition for constructive interference for light in air (not glass), we can set n = 1 in the above equation: 
2d = (m + 1/2)λ

Therefore, the correct choice is D.

Two Parallel Glass Plates of Index of Refraction N Are λ\lambdaλ

Two Parallel Glass Plates of Index of Refraction N Are $\lambda$