Time taken by light to travel in two different materials A and B of refractive indices  ${\mathrm{\mu }}_{\mathrm{A}} \mathrm{and} {\mathrm{\mu }}_{\mathrm{B}}$ of same thickness is t₁ and t₂ respectively. If ${\mathrm{t}}_2-{\mathrm{t}}_1=5\times {10}^{-10} \mathrm{s}$ and the ratio of ${\mathrm{\mu }}_{\mathrm{A}} \mathrm{to} {\mathrm{\mu }}_{\mathrm{B}}$ is 1 : 2. Then the thickness of material, in meter is : (Given v_A and v_B are velocities of light in A and B materials respectively).