Consider a thin square sheet of side L and thickness t, made of a material of resistivity ρ. The resistance between two opposite faces, shown by the shaded areas in the figure is____?

As R = ρl/a, where R is resistance, ρ is resistivity, l is length, and a is cross-sectional area. In this case, the length l is equal to the thickness t, and the cross-sectional area a is equal to L². Therefore, R = ρt/L². Hence R is independent of L.