Title: ETH_Sem3 / Physik_III / Woche1

Q: How is the optical path length defined?
A: \[D=nd\]\(D\) is the optical path length
\(n\) is the refractive index
\(d\) is the physical path length

Q: What is the speed of light? (as an equation, not \(c\))
A: \[v=\lambda\nu\]\(\lambda\) is the wavelength
\(\nu\) is the frequency

Q: What changes when light propagates between materials with different refractive indices?
A: Only the wavelength changes, the frequency stays the same.
The frequency stays the same \(\Rightarrow\) the lightwave stays in sync at the boundary
(And obviously speed accordingly)

Q: What is Fermat's principle?
A: Light traveling between two points will follow a path whose optical path length is extremal to variations in the path length.

Q: Is the light path always minimal?
A: Not necessarily: it must be locally extremal

Q: When is the optical path extremal?
A: \[\frac{d}{dx}D(x)\bigg\rvert_{x=\ldots}=0\]

Q: Snell's Law
A: \[n_1\sin\theta_1 = n_2\sin\theta_2\]

Q: How is the refractive index of a material defined?
A: \(n=\frac{c}{v}\geq 1\)