Time taken by light to travel in two different materials $A$ and $B$ of refractive indices $\mu_{A}$ and $\mu_{B}$ of same thickness is $t_{1}$ and $t_{2}$ respectively. If $t_{2}-t_{1}=5 \times 10^{-10}$ s and the ratio of $\mu_{A}$ to $\mu_{B}$ is $1: 2$. Then, the thickness of material, in meter is: (Given $v_{\mathrm{A}}$ and $v_{\mathrm{B}}$ are velocities of light in $A$ and $B$ materials respectively.)