An air filled cylindrical capacitor (capacitance C₀) of length L, with a and b as its inner and outer radii, respectively, consists of two coaxial conducting surfaces. Its cross-sectional view is shown in Fig. (i). In order to increase the capacitance, a dielectric material of relative permittivity ε_r is inserted inside 50% of the annular region as shown in Fig. (ii). The value of ε_r for which the capacitance of the capacitor in Fig. (ii), becomes 5C₀ is