As a physics student, I was taught that refraction happens because when light approaches a material with a refraction index that is different than the index of the medium it is travelling through at that moment, the light that hits it first, as shown here: This raises to me two questions: 1) From this explanation it follows that waves that come perpendicular to the surface should not 'bend'. That is however not what I have seen personally. How can that be explained? (I gather from that that such drawings are merely analogies and should not be taken literally, but that doesn't give me a full explanation) 2) What happens when single photons hit the material? Will they 'bend' as well?