Hello there! I have a couple of questions regarding light(EMR) and how it behaves when moving from one medium to another. From what I understand, the frequency of any light wave, when it moves from one medium to another, stays the same. As a consequence of this, the velocity of the light becomes proportional to the wavelength. When white light hits a prism, it is refracted or dispersed into different rays of different wavelength( the rainbow). Light with shorter wavelength refracts and is slowed down to a greater extent than light with longer wavelengths. Thanks to my new found knowledge in regards to light, I know have a few frustrating questions that I need to get off my chest. First of all, why does light refract in the first place when entering a medium from a vacuum, for example? In other words, what causes it to slow down and change direction? Second, why does light of shorter wavelength have a slightly different index of refraction when entering the same medium of light with a longer wavelength, or what does the frequency of this shorter wavelength light have to do with affecting it in such a manner to have a "greater" impact on it's speed and change in direction? Finally, what exactly are quanta. Yes, I know from the Wikipedia definition, that quanta are "discrete packets of energy", but, what exactly does this mean? Thank you for all your help!