Chapter 23, Problem 1RQ

To determine

Speed of light.

Answer to Problem 1RQ

The speed of light is $0.5\text{times}$ speed in the vacuum.

Explanation of Solution

Write the expression for refractive index.

  $n=\frac{c}{v}$        (I)

Here, $n$ is the refractive index, $c$ is the speed of light in vacuum and $v$ is the speed of light in the medium.

Rewrite the above expression to find $v$.

  $v=\frac{c}{n}$        (II)

Conclusion:

Substitute $2$ for $n$ in equation (II) to find $v$

  $\begin{array}{c}v=\frac{c}{2}\\ =\frac{1}{2}c\\ =0.5c\end{array}$

Therefore, the speed of light is $0.5\text{times}$ speed in the vacuum.