It is found that all electromagnetic signals sent from A towards B reach point C. The speed of electromagnetic signals in glass cannot be: |
A) \[1.0\times {{10}^{8}}m/s\]
B) \[2.4\times {{10}^{8}}m/s\]
C) \[2\times {{10}^{7}}m/s\]
D) \[4\times {{10}^{7}}m/s\]
Correct Answer: A
Solution :
[a] This is a case of total internal reflection. |
\[\therefore \] \[\theta >{{\theta }_{c}}(={{\sin }^{-1}}\frac{1}{\mu })\] |
\[\frac{1}{\mu }<\sin \theta \]\[\frac{1}{\mu }<\sin 45{}^\circ \] |
\[\mu >1/\sin 45{}^\circ \]\[\mu >\sqrt{2}\] |
As \[v=\frac{c}{\mu }\] |
\[v<\frac{c}{\sqrt{2}}=\frac{3\times {{10}^{8}}}{\sqrt{2}}\] |
\[v<2.1\times {{10}^{8}}\] |
\[\therefore \] only (2) is not possible. |
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