Question

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Answer 1

A ray of light in air is incident on an air-to-glass boundary at an angle of 30 degrees ... If the critical angle for internal reflection inside a certain transparent material is ... from the opposite side into air at what angle to the normal to that surface? ..... TIR can only occur when light approaches a boundary

the phenomenon of total internal reflection was introduced. Total internal reflection (TIR) is the phenomenon that involves the reflection of all the incident light off the boundary. TIR only takes place when both of the following two conditions are met:

a light ray is in the more dense medium and approaching the less dense medium.
the angle of incidence for the light ray is greater than the so-called critical angle.
In our introduction to TIR, we used the example of light traveling through water towards the boundary with a less dense material such as air. When the angle of incidence in water reaches a certain critical value, the refracted ray lies along the boundary, having an angle of refraction of 90-degrees. This angle of incidence is known as the critical angle; it is the largest angle of incidence for which refraction can still occur. For any angle of incidence greater than the critical angle, light will undergo total internal reflection.