A) \[1.5\times {{10}^{8}}m/s\]
B) \[3\times {{10}^{8}}m/s\]
C) \[0.75\,m/s\]
D) \[6\times {{10}^{8}}\,m/s\]
Correct Answer: A
Solution :
Critical angle \[C={{30}^{o}}\](given) From the law of total internal reflection we have \[\sin C=\frac{\upsilon }{c}\] \[\sin {{30}^{o}}=\frac{\upsilon }{c}\] \[0.5=\frac{\upsilon }{3\times {{10}^{8}}}\] \[\upsilon =0.5\times 3\times {{10}^{8}}=1.5\times {{10}^{8}}\,m/s\]
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