A) 3500\[\overset{0}{\mathop{A}}\,\]
B) 4200\[\overset{0}{\mathop{A}}\,\]
C) 4700\[\overset{0}{\mathop{A}}\,\]
D) 6000\[\overset{0}{\mathop{A}}\,\]
Correct Answer: B
Solution :
The condition for minima is given by \[d\sin \theta =n\lambda \] For n = 1, we have \[d\,\sin \theta =\lambda \] If angle is small, then \[\sin \theta =\theta \] \[\Rightarrow \] \[d\theta =\lambda \] Half angular width \[\theta =\frac{\lambda }{d}\] Full angular width \[2\theta =2\frac{\lambda }{d}\] Also \[\omega =\frac{2\lambda }{d}\] \[\therefore \] \[\frac{\lambda }{\lambda }=\frac{\omega }{\omega }\]or \[\lambda =\lambda \frac{\omega }{\omega }\] or \[\lambda =6000\times 0.7\] \[=4200\overset{\text{o}}{\mathop{\text{A}}}\,\]
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