A) \[2.945\times {{10}^{-7}}m\]
B) \[3.945\times {{10}^{-7}}m\]
C) \[4.945\times {{10}^{-7}}m\]
D) \[1.945\times {{10}^{-7}}m\]
Correct Answer: A
Solution :
Given:\[\mu \]for air\[=1,\,\,\lambda =5890\overset{\text{o}}{\mathop{\text{A}}}\,\]\[=5.89\times {{10}^{-7}}\,\,m,\,\,r=0\]. The condition for destructive interference in reflected light \[2\mu t\cos r=n\lambda \] For minimum thickness\[n=1\], so,\[2\mu t\cos r=n\lambda \] or \[t=\frac{\lambda }{2\mu \,\,\cos r}=\frac{5.89\times {{10}^{-7}}}{2\times 1\times 1}\] \[=2.945\times {{10}^{-7}}m\]
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