A) \[8\times {{10}^{-11}}s\]
B) \[2\times {{10}^{-11}}s\]
C) \[8\times {{10}^{-8}}s\]
D) \[2\times {{10}^{-8}}s\]
Correct Answer: B
Solution :
From Hugen's principle of wave theory, we have \[_{1}{{n}_{2}}=\frac{{{v}_{1}}}{{{v}_{2}}}=\frac{speed\text{ }of\text{ }light\text{ }in\text{ }first\text{ }medium}{speed\text{ }of\text{ }light\text{ }in\text{ }second\text{ }medium}\] Given, \[{{n}_{2}}=1.5,v=3\times {{10}^{8}}m/s\] \[\therefore \] \[{{v}_{2}}=\frac{3\times {{10}^{8}}}{1.5}m/s\] \[Also\text{ }time=\frac{dis\tan ce}{speed}=\frac{4\times {{10}^{-3}}\times 1.5}{3\times {{10}^{8}}}\] \[T=2\times {{10}^{-11}}s\] Alternative: Time taken to cross the glass slab \[T=\frac{nd}{c}=\frac{1.5\times 4\times {{10}^{-3}}}{3\times {{10}^{8}}}\] \[=2\times {{10}^{-11}}s\]
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