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A glass surface is coated by an oil film...

A glass surface is coated by an oil film of uniform thickness `1.00xx10^-4`cm. The index of refraction of the oil is 1.25 and that of the glass is 1.50. Find the wavelengths of light in the visible region `(400nm-750nm) `which are completely transmitted by the oil film under normal incidence.

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The correct Answer is:
A, D
For the thin oil film
`d=1xx10^-4cm`
`10^-6m`
`mu_(oil)=1.25 and mu`
`=1.50`
`lamda(2mud)/((n+1/2))
`=(2xx10^-6xx(1.25)xx2)/((2n+1))`
`=(5xx10^-6m)/(2n+1)`
`rarr lamda=(5000nm)/(2n+1)`
` For the wavelength is the region
(400nm-750 nm)
when n=3,
`lamda=5000-(2xx3+1)
`5000/7=714.3`
when n=4
`lamda=5000/(2xx4+1)`
`=5000/9=555.6nm`
`when n=5
lamda=5000/(2x5+1)`
=5000/11=454.5nm`
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