An electromagnetic wave , whose wave normal makes an angle of `45^(@)` with the vertical , travelling in air strikes a horizontal liquid surface . While travelling through the liquid it gets deviated through `15^(@)` . What is the speed of the e.m. wave in the liquid , if the speed of electromagnetic wave in air is `3xx 10^(8)`m/s ?

Options

A. `1.5 xx 10^(8)` m/s
B. `2.1 xx 10^(8) ` m/s
C. `2.5 xx 10^(8)` m/s
D. `(sqrt2)/(3) xx 10^(8)` m/s

Answer

B

Explanation

`i=45^(@) , delta = i-r therefore 45^(@)- 15 = 30^(@)`
`therefore (sin i)/(sin r) = (1)/((sqrt2)/(1//2)) = (2)/(sqrt2) = sqrt2`
`therefore sqrt2 = (V_(1))/(V_(2)) therefore V_(2) = (V_(1))/(sqrt2) = (3 xx 10^(8))/(1.414)`
`therefore V_(2) = 2.1 xx 10^(8) ` m/s