A) 0.65 mm
B) 1.30mm
C) 1.62 mm
D) 1.95mm
Correct Answer: C
Solution :
[c] Given\[d=1mm,\,\,\,\lambda =6.5\times {{10}^{-7}}m,\,\,\,D=1m\] For \[{{n}^{th}}\]dark fringe \[{{y}_{n}}=\left( \frac{2n-1}{2} \right)\frac{D\lambda }{d}\] For third fringe, \[{{y}_{3}}=\left( \frac{2\times 3-1}{2} \right)\times \frac{1\times 6.5\times {{10}^{-7}}}{1\times {{10}^{-3}}}=1.625mm\].
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