Refractive index from speed

Problem

Light travels through a glass at $v = 2{,}0\cdot 10^8\;\mathrm{m/s}$. Calculate the refractive index and identify the type of glass.

Solution

Setup. The refractive index is the ratio of the speed of light in vacuum to that in the medium:

$n = \frac{c}{v}$

with $c = 3{,}0\cdot 10^8\;\mathrm{m/s}$.

Substitution.

$n = \frac{3{,}0\cdot 10^8}{2{,}0\cdot 10^8}$

$\ev{n = 1{,}5}$

An index $n \approx 1{,}5$ is typical of ordinary crown glass (common window and lens glass). Light in the glass travels at two thirds of its vacuum speed.

Linked atoms

Topics: Ottica Concepts: Rifrazione e legge di Snell Skills: Analisi dimensionale