A) \[{{10}^{-11}}s\]
B) \[2\times {{10}^{-11}}s\]
C) \[2\times {{10}^{11}}s\]
D) \[2\times {{10}^{-5}}s\]
Correct Answer: B
Solution :
We know, \[{{n}_{a}}{{c}_{a}}={{n}_{g}}{{c}_{g}}\] \[\frac{{{n}_{g}}}{{{n}_{a}}}=\frac{{{c}_{a}}}{{{c}_{g}}}\] \[\frac{3}{2}=\frac{3\times {{10}^{8}}}{{{c}_{g}}}\] \[{{c}_{g}}=2\times {{10}^{8}}\] We have. \[\text{Time=}\frac{\text{Distance}}{\text{Speed}}\] \[\text{t}\,\text{=}\frac{4\times {{10}^{-3}}}{2\times {{10}^{8}}}\] or \[t=2\times {{10}^{-11}}s\]
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