A parallel plate capacitor with plate area A and plate separation d, with a vacuum between the plates, has a capacitance C_0. 

The space between the plates is filled with two slabs of the same area but thicknesses (d/4) and (3d/4) made of material of dielectric constant 2 and 4, respectively. The capacitance of the capacitor is now:

Concept:

• Capacitor: 
  • ​A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other.
  • It is a passive electronic component with two terminals.
• ​Parallel plate capacitor: 
  • ​When two parallel plates are connected across a battery, the plates are charged and an electric field is established between them, and this setup is known as the parallel plate capacitor.
  • The capacitance of the parallel plate capacitor,  where, A = area, d = distance between two plates
  • When a dielectric slab for dielectric constant k, then the capacitance of the parallel plate capacitor, 
• Capacitance in parallel combination:
  • ​Equivalent capacitance, C_eq = C₁ + C₂
• Capacitance in series combination:
  • ​Equivalent capacitance,  

Calculation:

In parallel plate capacitors, the capacitance in air,  . . . . . . . . . .(1)

When the dielectric slab is inserted, the capacitance, 

Now, the space between the plates is filled with two slabs of the same area but thicknesses (d/4) and (3d/4) made of material of dielectric constant 2 and 4, respectively. The capacitors are in a series combination.

So, Equivalent capacitance, 

Substitute equation (1) in the above, we get