It is found that all electromagnetic signals sent from A towards B reach point C inside the glass sphere, as shown in figure. The speed of electromagnetic signals in glass cannot be:

Options

A. `1.0xx10^(8)ms^(-1)`
B. `2.4xx10^(8)ms^(-1)`
C. `2xx10^(7)ms^(-1)`
D. `4xx10^(7)ms^(-1)`

Answer

b.

Explanation

This is a case of total internal reflection .
Here `theta=45^(@)` and `theta gt theta_(C)`
`rArr 45^(@) gt theta_(C)rArrsin45^(@) gt sintheta_(C)`
`rArr (1)/(sqrt(2)) gt (1)/(mu)`
`rArr mu gt sqrt(2)" " ("As " v=c/mu)`
`rArr (c)/(v) gt sqrt(2)`
`v lt (c)/(sqrt(2))=(3xx10^(8))/(sqrt(2))rArrvlt2.1xx10^(8)`
Only (b) is not possible.