Two parallel plate capacitors \( C_{1} \) and \( C_{2} \) each having capacitance of \( 10 \, \mu \text{F} \) are individually charged by a \( 100 \, \text{V} \) D.C. source. Capacitor \( C_{1} \) is kept connected to the source and a dielectric slab is inserted between it plates. Capacitor \( C_{2} \) is disconnected from the source and then a dielectric slab is inserted in it. Afterwards the capacitor \( C_{1} \) is also disconnected from the source and the two capacitors are finally connected in parallel combination. The common potential of the combination will be ______ V.
