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A parallel beam of light of wavelength 5...

A parallel beam of light of wavelength 560 nm falls on a thin film of oil (refractive index = 1.4). What should be the minimum thickness of the film so that it strongly reflects the light ?

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Given that `lamda=560xx10^-9m, mu=1.4`
For strong reflection
`2mud=(2n+1)lamda/2`
`rarr mu=(2n+1)lamda(4d)` ltbr,. `rarr d=(2n+1)1/(4mu)`
for miimum thicknes putting n=0
`rarr d=lamda/(4d)`
`rarr d=(560xx10^-9)/14`
`10^-7m=100nm`
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