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Find the minimum thcknessof a film which...

Find the minimum thcknessof a film which will strongly reflect the light of wavelength 589 nm. The refractive index of the material of the film is 1.25.

A

`118nm`

B

`120nm`

C

`118m`

D

`188nm`

Text Solution

Verified by Experts

For strong reflection, the least optical path difference introduced by the film should be `lambda//2`. The optical path difference the waves reflected from the surfaces of the film is `2mu d`.
Thus, for strong reflection,
`2mu d =lambda//2`
`d=lambda/(4mu)=589/(4xx1.25)=118 nm`.
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