The distance between two plates of a capacitor is \( d \) and its capacitance is \( C_1 \), when air is the medium between the plates. If a metal sheet of thickness \( {2d}/{3} \) and of the same area of plate is introduced between the plates, the capacitance of the capacitor becomes \( C_2 \). The ratio \( {C_2}/{C_1} \) is:
