Binoculars and microscopes are frequently made with coated optics by adding a thin layer of transparent material to the lens surface as shown, in order to improve light transmission. One wants:
A) constructive interference between waves 1 and 2
B) destructive interference between waves 3 and 4
C) constructive interference between waves 3 and 4
D) the coating to be more transparent than the lens
E) the speed of light in the coating to be less than that in the lens

Question

Binoculars and microscopes are frequently made with coated optics by adding a thin layer of transparent material to the lens surface as shown, in order to improve light transmission. One wants: 
A) constructive interference between waves 1 and 2 
B) destructive interference between waves 3 and 4 
C) constructive interference between waves 3 and 4 
D) the coating to be more transparent than the lens 
E) the speed of light in the coating to be less than that in the lens

Quizplus · Accepted Answer

Constructive interference between waves 3 and 4 is important for coated optics because it allows for more light to pass through the lens. The coating helps to reduce the amount of reflected light, which causes destructive interference between waves 1 and 2. Also, the coating material should have a refractive index that is intermediate between that of the lens and air so that there is constructive interference between waves 3 and 4, leading to increased light transmission. Therefore, choice C is the best option as it correctly identifies the importance of constructive interference between waves 3 and 4.

Binoculars and Microscopes Are Frequently Made with Coated Optics by Adding