1.

A parallel beam of sodium light of wavelength `6000 Å` is incident on a thin glass plate of `mu=1.5`, such that the angle of refraction in the plate is `60^(@)`. The smallest thickness of the plate which will make it appear dark by reflected light isA. 3926 Ã…B. 4353 Ã…C. 1396 Ã…D. 1921 Ã…

Answer» Correct Answer - A
The condition for minimum thickness corresponding to a dark band is, `2mu t" cos"r=lambda`
` :. t=(lambda)/(2mu"cos"r)=(5890xx10^(-10))/(2xx1.5xx"cos"60^(@))`
` " "=3926xx10^(-10)m=3926Ã…`


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