A) 8 mm
B) 6 mm
C) 4 mm
D) 3 mm
Correct Answer: B
Solution :
Given \[{{\lambda }_{1}}=12000\,\overset{\text{o}}{\mathop{\text{A}}}\,\]and \[{{\lambda }_{2}}=10000\,\overset{\text{o}}{\mathop{\text{A}}}\,,\] \[D=2\,cm\]and \[d=2\,mm=2\times {{10}^{-3}}\,cm.\] We have \[\frac{{{\lambda }_{1}}}{{{\lambda }_{2}}}=\frac{{{h}_{2}}}{{{h}_{1}}}\] \[=\frac{12000}{10000}=\frac{6}{5}\] as \[x=\frac{{{u}_{1}}{{\lambda }_{1}}D}{d}=\frac{5\times 12000\times {{10}^{-10}}\times 2}{2\times {{10}^{-3}}}\] \[=5\times 1.2\times {{10}^{4}}\times {{10}^{-10}}\times {{10}^{3}}=6\,mm\]
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