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Question
What is optical path? Obtain the equation for optical path of a medium of thickness d and refractive index n.
Solution
- Optical path of a medium is defined as the distance d’ light travels in vacuum at the same time it travels a distance ‘d’ in the medium.
- n = refractive index.
- d = thickness
ν = speed of light in the medium
v = `"d"/"t" ("or") "t" = "d"/"v"`
c = `("d"')/"t"` or t = `("d"')/"c"`
as time is same
`("d"')/"c" = "d"/"v"`
d' = `"c"/"v"`d
d' = nd
∵ n = `"c"/"v"`
As ‘n’ is always greater than 1, the optical path d’ of the medium is always greater than 1.
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