Optical physics. Explaining and what Refraction, total internal reflection and dispersion is. Refraction is the bending of the light rays path, when it passes a new medium. When the index of refraction is greater in the new medium and the angle is great, it will reach the critical angle and undergo internal reflection. Dispersion happens because a light wave contains all wavelength of visible color. And some materials index of refraction depends on the frequency. So the light wave will have different path for each wavelength. This video is for helping understand my videos about rainbows and mirages.