I know capacitors have 2 plates, and an insulator in between the plates. I am wondering what elements inside of a capacitor make the capacitance larger, and what makes the maximum voltage higher?


3 Answers 3


\$ C = \epsilon_0 \epsilon_r \dfrac{A}{d}\$


  • \$C\$ is the capacity in Farad [F];
  • \$\epsilon_0=8.854×10^{−12} \text{F/m}\$;
  • \$\epsilon_r\$ is 'relative permittivity', its value is specific for the material used as insulator. See also @rawbrawb's comment;
  • \$A\$ is the area of the plates that overlaps in square meters;
  • \$d\$ is the distance between the plates in meters.


  • if the plate overlapping area increases, the capacity increases and
  • if the distance between the plates increases, the capacity decreases.

The insulator that fills the space between both plates (A×d) has a limited strength when it comes to voltage between the plates. The insulator will breakdown at a certain maximum voltage, at that point it is no longer a capacitor, but probably a short.

  • 2
    \$\begingroup\$ To add to Jippie's answer, \$\epsilon_r\$ is a "large dial" that can be turned. Some materials have \$\epsilon_r\$ that are high, TiO2 = 100, SiO2 = 3.8 and some materials actually prevent the breakdown between the plates enabling even higher voltages. \$\endgroup\$ Apr 12, 2013 at 22:35

http://en.wikipedia.org/wiki/Capacitance especially "Capacitance of simple systems": larger plate area and smaller separation will give greater capacitance.

The maximum voltage depends on the breakdown voltage of the dielectric (material between plates); the point at which it stops being an insulator. For any given dielectric, the breakdown voltage is proportional to its thickness (i.e., the plate separation).


If you want to have voltage higher, you need to have larger space among plates. But this is opposite to another request to have higher capacitance. So what you can do is to separate plates more to have higher voltage standing and to increase area of the plates in order to increase capacitance as well.


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