A) 500 nm
B) 600 nm
C) 400 nm
D) 300 nm
Correct Answer: C
Solution :
Fringe width\[W=\frac{D\lambda }{d}\] Given, \[d=0.4\text{ }mm=0.04\text{ }cm,\text{ }D=200\text{ }cm\] \[W=2\text{ }mm=0.2\text{ }cm\] \[\therefore \] \[0.2=\frac{200\times \lambda }{0.04}\]\[\Rightarrow \]\[\lambda =400\,nm\]
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