Light and Optics in Physics

Light is the one part of physics you can watch happening, and almost all of it follows from a single number attached to each material. The index of refraction measures how much slower light travels inside a medium than in vacuum, and the two laws of direction change fall straight out of that speed difference. Reflection keeps the speed and mirrors the angle, while refraction changes both the speed and the direction, bending the ray towards the normal whenever it enters something denser. Push that bending far enough and the light stops leaving the medium altogether, which is what keeps a signal inside a glass fibre. The blocks give the definition of the index, both laws in the forms you need for solving, the critical angle where refraction gives way to reflection, and the three ideas that sit behind them, the ray approximation, Huygens's wavelets and dispersion.