Refraction and Lenses - Mission RL5 Detailed Help


The diagrams show incident rays approaching a boundary with a second medium. The relative speed of light (v) in the two media is indicated. In which diagram(s) will total internal reflection occur (provided that the angle of incidence is sufficiently large)?


 
Requirements for Total Internal Reflection (TIR):
Two requirements must be met for total internal reflection to occur. First, light must be in the more dense medium heading toward the boundary with the least dense medium. Second, light must be approaching the boundary with an angle of incidence that is greater than the value of the so-called critical angle.


 
As mentioned in the Know the Law section above, TIR can only take place provided that the incident ray is traveling within the more dense medium. The optical density of a medium is related to the speed at which light travels through that material (see Know the Law section below). To be successful on this question, you will have to inspect each diagram carefully to determine if it satisfies the condition of light being in the more dense medium and heading towards the least dense medium.


 
Optical Density and the Speed of Light:
The speed at which light travels through a medium is dependent upon the optical density of that medium. Light travels fastest in media that are least optically dense.