Chad provides a thorough lesson on Reflection and Refraction. The lesson begins with the Law of Reflection which simply states that the angle of incidence equals the angle of reflection. The rest of the lesson is devoted to refraction, the bending of light as it is transmitted from one medium to another. The speed of light is different in different mediums, and the index of refraction is a measure reflecting this change, as it is the ratio of the speed of light in a vacuum relative to the speed of light in a medium. As the speed of light in any medium is always slower than the speed of light in a vacuum, indexes of refraction are always greater than 1.
Snell's Law of Refraction allows for the calculation of the angle of refraction as light passes from one medium to the next based upon each medium's index of refraction. When light passes from a medium with a lower index of refraction to one with a higher index of refraction, it bends towards the normal to the surface. When light passes from a medium with a higher index of refraction to one with a lower index of refraction, it bends away from the normal to the surface. Chad solves several examples of reflection and refraction calculations.
Total internal reflection is then discussed which is only possible when light travels from a medium with a higher index of refraction to one with a lower index of refraction. Beyond some minimum angle of incidence, the angle of refraction would be equal to or exceed 90 degrees meaning no light is actually transmitted into the next medium and is therefore only reflected at the interface between the two mediums. This minimum angle of incidence is called the critical angle.
The lesson concludes with brief discussion of dispersion which results from the fact that different wavelengths of light will travel through the same medium with slightly different speeds and therefore have a slightly different index of refraction. As a result, if white light, which is a combination of all visible wavelengths, undergoes refraction, the angle of refraction will be slightly different for the different wavelengths resulting in their separation as seen when white light passes through a prism.
00:00 Lesson Introduction
01:06 Law of Reflection
02:32 Refraction and Index of Refraction
08:22 Snell's Law of Refraction
13:48 Reflection and Refraction Practice Problems
24:58 Total Internal Reflection
30:19 Dispersion
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