Chapter 20, Problem 20.22P

(a)

Interpretation Introduction

Interpretation:

The critical value of ${\text{θ}}_{\text{i}}$ has to be calculated.

Concept introduction:

The angle of incidence is bigger than this critical angle, the refracted ray will not emerge from the medium, however will be reflected back into the medium.

This is called total internal reflection.

Snell’s law:

${\text{n}}_0\text{sin}i\text{=}{\text{n}}_1\text{sin}\text{θ}$

${\text{n}}_{\text{1}}\text{and}{\text{n}}_{\text{2}}$ are the refractive indexes of the two media

$\begin{array}{l}\text{sin}{\text{θ}}^{\text{`}}{}_{\text{c}}{\text{=n}}_{\text{2}}\text{sin90}\\ \text{sin}{\text{θ}}^{\text{`}}{}_{\text{c}}\text{=}\frac{{\text{n}}_{\text{1}}}{{\text{n}}_{\text{2}}}\end{array}$

The angle of incidence is equal to the angle of reflection by the light is reflected.

(b)

Interpretation Introduction

Interpretation:

The quotient power out/power has to be calculated.

Concept introduction:

The quotient power out/power can be calculated using below formula

$\frac{\text{Power}\text{out}}{\text{Power}\text{in}}{\text{=10}}^{\text{-l(dB/m/10)}}$

$\text{dB/m}\text{=}\text{decibel}\text{per}\text{meter}$

$\text{l=}\text{an}\text{optical}\text{fiber}\text{of}\text{length}$