# Parrallel Plate Capacitors

1. Sep 12, 2008

If two dielectric materials with dielectric constants k1 and k2 and thickness d1 and d2 are within two copper plates, how do you obtain a capacitance given that the cross sectional areas are all the same?

2. Sep 12, 2008

### atyy

Treat them in series.

3. Sep 12, 2008

### atyy

Actually, it depends whether they are in parallel or in series.

4. Sep 13, 2008

Thanks for the reply but,

The two dielectrics are within one dielectric field capacitor, s how do we find the capacitance if both dielectrics are placed in between the plates?

5. Sep 13, 2008

### atyy

If the two dielectrics are placed in series, ie. one dielectric fills part of the distance, and the other fills the rest of the distance, then you treat them as two capacitors in series, each having a different dielectric constant.

If the two dielectrics are in parallel, ie. both fill the entire distance between the plates, but each only contacts part of the area of a plate, then you treat them as two capacitors in parallel (remembering to take into account that capacitance depends on the area of the plates).

6. Sep 13, 2008

### Defennder

As he said, you need to tell us if the dielectrics are sandwiched in series or in parallel.

7. Sep 13, 2008

### atyy

Oh, I see d1 and d2 such that the total distance between the plates d= d1+d2. So they are just two capacitors in series.

The capacitance of one capacitor is C=kA/d, where k is related to the dielectric constant (look it up).

The capacitor of two capacitors in series is C=C1C2/(C1+C2).