A parallel plate air condenser has a capacity of 4 μF. It is filled with two different dielectrics of constants 4 and 6 and they fill the upper and lower halves of the space as shown. The capacity now will be
20 μF
Visualise two condensers each with plate area half that of the original condenser. So each will have a capacity 2 μF without dielectric. Now because of the dielectrics, the upper one is 12 μF and lower one is 8 μF and they are parallel.