A) 30 nm
B) 60 nm
C) 90 nm
D) 120nm
Correct Answer: C
Solution :
Given \[\mu =\] refractive index of glass = 1.5 t = thickness of coating, \[\mu =\] refractive index of coating \[=1.8\,\lambda =648\times {{10}^{-9}}m\] For constructive interference \[2\mu t=(2n+1)\frac{\lambda }{2}\] \[2\times 1.8\times t=\frac{648\times {{10}^{-9}}}{2}\](t to be minimum n = 0) \[t=\frac{648}{2\times 2\times 1.8}\times {{10}^{-9}}m\] \[t=\frac{648}{7.2}\times {{10}^{-9}}m=90\,m\]You need to login to perform this action.
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