Solution to 1986 Problem 3

The speed of electromagnetic radiation in matter is

\begin{align*}v = \frac{c}{n} = \frac{c}{\displaystyle \sqrt{\frac{\epsilon \mu}{\epsilon_0 \mu_0}}} = \frac{c}{\sqrt{\epsilo...
\epsilon_r, the relative permittivity (also known as the dielectric constant), is 2.1 and \mu_r, the relative permeability, is 1.0, so

\begin{align*}v = \frac{c}{\sqrt{2.1 \cdot 1.0}} = \boxed{\frac{c}{\sqrt{2.1}}}\end{align*}
Hence, answer (D) is correct.

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