Figure 2-36. Total internal reflection in 90-degree prism.

TM 9-258

f. At any boundary between different media there

water,n=1. 333 (para 2-12c), sin

For

is both reflection and refraction of an incident ray,

1= 0. 750187, and the critical angle

excepting total reflection (para 2-7f). Figures 2-35 and 2-

1. 333

r = 48 36 min (para 2-17a).

36, therefore, are only approximations.

g. The critical angle of any substance can be easily

calculated from the equation of Snell's law

2-17. Critical Angles of Various Substances.

(para 2-11. e), n =sin n

a. The critical angles for various substances, when

sin r

the external medium is air, are as follows:

It follows that:

Water ...................................................... 48 36 min

sin r = sin 90 = 1

Crown glass ............................................ 41 18 min

Quartz ..................................................... 40 22 min

Flint glass ................................................ 37 34 min

Diamond .................................................. 24 26 min

2-25