What is the critical angle for total internal reflection in most glass? a. 90 degrees c. 180 degrees b. 45 degrees d. 42 degrees

Answer;

d. 42 degrees

Explanation; Critical angle is defined as the angle of incidence that provides an angle of refraction of 90-degrees. in other words, the critical angle is the Θi or the angle of incidence that gives a Θr or the refraction angle value of 90-degrees. The actual value of the critical angle is dependent upon the two materials on either side of the boundary. For the crown glass-air boundary, the critical angle is approximately 42 degrees.