Question

19. A thin film of soup voluton = 14) les on
the top of a glass plate=5 When visible
lught is incident almost normal to the plate, two
adjacent reflection maxima se observed at two
wavelengths 400 and 630 mm The munimum
thickness of the soap soluton is
1) 420 nm
2) 450 mm
3) 630 nm
4 1260 nm​

Answer 1

C O N C E P T :

waves optics

AnSwER :-

Options 2) 450 nm is right Answer

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C O N C L U S I O N :

For reflection at the air-soap solution interface, the phase difference is π.

For reflection at the interface of soap solution to glass also, there will be a phase difference of π.

: $\implies$ For Maximum intensity: 2μt=nλ

: $\implies$ For n, nλ1=(n−1)λ2

: $\implies$ or n×420 = (n−1)630

or n = 3

: $\implies$ Maximum order, where they coincide

: $\implies$ so, 2×1.4×t = 3×420

or t = 450 nm

∴ 4550 nm

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Hope it's helps !!