Three identical capacitors C 1 , C 2 a n d C 3 have a capacitance of 1.0 μ F each and they are uncharged…

Three identical capacitors $C_1,C_2 \mathrm{a}\mathrm{n}\mathrm{d} C_3$ have a capacitance of $1.0 \mu F$ each and they are uncharged initially. They are connected in a circuit as shown in the figure and $C_1$ is then filled completely with a dielectric material of relative permittivity ${ϵ}_r$ . The cell electromotive force (emf) $V_0 = 8 V$ . First the switch $S_1$ is closed while the switch $S_2$ is kept open. When the capacitor $C_3$ is fully charged, $S_1$ is opened and $S_2$ is closed simultaneously. When all the capacitors reach equilibrium, the charge on $C_3$ is found to be $5 \mu C$ . The value of ${ϵ}_r$ =____________.