We know that resistance is dependent on both the materials resistivity and the geometry of the material. For a cylindrical or rectangular material the resistance is:


where l is the length and A the cross-sectional area.

In the same manner I understand that permittivity is a measure of how an electric field affects, and is affected by, a dielectric medium. When I look at capacitance I can see that it is dependent on the permittivity and the geometry. An example is the parallel plate capacitor's capacitance:


where A is the area of the plates/dielectric and d the distance between the conductive plates.

Is capacitance the same as "permittance"? If not, what is the geometry dependent permittivity?

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    \$\begingroup\$ Permittance was a word used by Heaviside for what we now call susceptance which is the imaginary part of admittance (the real part being conductance), which in turn is the inverse of impedance. en.wikipedia.org/wiki/Oliver_Heaviside \$\endgroup\$ Apr 8, 2014 at 17:35
  • \$\begingroup\$ @SpehroPefhany: It would make more sense to still use this word as far as I understand. Thanks for letting me know it was actually a word named permittance. \$\endgroup\$ Apr 8, 2014 at 23:04

1 Answer 1


Look at the unit analysis: Resistivity is measured in Ω-m. When you mutliply by length (m) and divide by area (m2), you're left with just Ω.

Permittivity is measured in Farads/m. When you multiply by area (m2) and divide by spacing (m), you're left with just Farads, or capacitance.


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