Two coaxial cables $1$ and $2$ are filled with different dielectric constants $\varepsilon_{r 1}$ and $\varepsilon_{r 2}$ respectively. The ratio of the wavelengths in the two cables, $\left(\lambda_{1} / \lambda_{2}\right)$ is
- $\sqrt{\varepsilon_{r 1} / \varepsilon_{r 2}}$
- $\sqrt{\varepsilon_{r 2} / \varepsilon_{r 2}}$
- $\varepsilon_{r 1} / \varepsilon_{r 2}$
- $\varepsilon_{r 2} / \varepsilon_{r 1}$