A) \[25{}^\circ \]
B) \[30{}^\circ \]
C) \[20{}^\circ \]
D) \[45{}^\circ \]
Correct Answer: A
Solution :
[a] \[d\sin {{\theta }_{2}}=2\lambda \] (for 2nd minima) \[\Rightarrow d\times \left( \frac{\sqrt{3}}{2} \right)=2\lambda ...(i)\] For first minima, \[d\sin {{\theta }_{1}}=\lambda \] \[\Rightarrow \sin {{\theta }_{1}}=\frac{\lambda }{d}=\frac{\sqrt{3}}{4}=0.43\] \[\Rightarrow {{\theta }_{1}}<30{}^\circ ,\Rightarrow {{\theta }_{1}}\approx 25{}^\circ \]
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