Speed of Light in Matter

Calculate the speed of light in zircon, a material used in jewelry to imitate diamond.

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

Strategy
The speed of light in a material, $v$ , can be calculated from the index of refraction $n$ of the material using the equation $n = c / v$ .
Solution
The equation for index of refraction states that $n = c / v$ . Rearranging this to determine $v$ gives
$v = \frac{c}{n} .$
25.5

The index of refraction for zircon is given as 1.923 in Table 25.1, and $c$ is given in the equation for speed of light. Entering these values in the last expression gives
$\begin{matrix} v & = & \frac{3.00 \times 10^{8} m/s}{1.923} \\ = & 1.56 \times 10^{8} m/s . \end{matrix}$
25.6
Discussion
This speed is slightly larger than half the speed of light in a vacuum and is still high compared with speeds we normally experience. The only substance listed in Table 25.1 that has a greater index of refraction than zircon is diamond. We shall see later that the large index of refraction for zircon makes it sparkle more than glass, but less than diamond.

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