Question

Light enters at an angle of incidence "i" in a transparent rod of refractive index (n) of the material of the rod. The light once entered into it will not leave it through its lateral face what so ever be the angle of incidence if:

• A. $n>\sqrt{2}$
• B. n = 1
• C. n = 1.1
• D. n = 1.3

Answer 1

The correct option is A $n>\sqrt{2}$


For TIR at B
$sin\theta =sinC,sin(90-r)>sinC.cosr>sinC......\left(1\right)$
By snell law
$1\times sini=nsinrsinr=\frac{sini}{n}cosr=\sqrt{1-\frac{si{n}^{2}i}{n^2}}>sinCOnsolving{n}^2>si{n}^{2}i+1$
$n>\sqrt{2}$ (for max value of sin i = 1)