start in the fascinating and wonderful world of electronics by learning the very primary basics - factors determining capacitance. The principal factors determining capacitance are the areas of the metallic plates themselves and any dielectric (non conducting material) between them

## WWW.ELECTRONICS-TUTORIALS.COM

Please visit VK2TIP's Book Shelf. My personal recommendations, thanks.

Friday, 29-Jun-2018 02:34:31 PDT

# FACTORS DETERMINING CAPACITANCE

•NEW! ‣ - Amazon Electronic Component Packs. Check out the Amazon Electronic Component Packs page.

### What are the factors determining capacitance?

The principal factors determining capacitance are the areas of the metallic plates themselves and any dielectric (non conducting material) between them.

Capacitance is directly proportional to plate area.

The formula for a two plate capacitor is C = 0.225KA / S where C is in pF, K is the dielectric constant (air = 1), A = area of the plates in square inches and S is the spacing between plates in inches. One inch = 25.4 mm or 2.54 cm.

If we had two metal plates each measuring 2" X 2" we have a net area of 4 inches square. Should the plates be separated by 1/100" then the capacitance exhibited would be:

C = ( 0.225 X 1 X 4 ) / 0.01 = 90 pF

For more than two plates the formula becomes C = 0.225KA (N - 1) / S where N = number of plates. This is the standard formula for air variable capacitors.

The dielectric constant K varies with the dielectric used. Some examples are:
Glass 4 - 7, Mica 5 - 7, Porcelin 6 - 7, Paper 2 - 3, Ceramics 3 - 7. Note the dielectric constant of solid dielectrics may vary with increasing frequency - an important property to remember.

### Mica, paper and electrolytics?

Capacitors were represented above as two or more parallel plates and some, such as mica or the old paper types, were made this way.

If we have a flexible dielectric then we can have two long sheets of thin metal foil separated by the thin flexible dielectric. In this way we can then roll up the foil / dielectric combination with a wire connected to one foil and another wire connected to the other foil. This is the basis of the modern electrolytic capacitor.

A modern electrolytic capacitor consists of an aluminium foil positive plate immersed in a solution called an "electrolyte" which is an ionised solution capable of carrying current. The aluminium foil is the positive plate and the electrolyte is the negative plate.

 Click image to print out a printer friendly version of this page.

Looking for more? Visit my site map page:

This site is hosted at Press Wizards for better value.

the author Ian C. Purdie, VK2TIP of www.electronics-tutorials.com asserts the moral right to be identified as the author of this web site and all contents herein. Copyright © 2000, all rights reserved. See copying and links. These electronic tutorials are provided for individual private use and the author assumes no liability whatsoever for the application, use, misuse, of any of these projects or electronics tutorials that may result in the direct or indirect damage or loss that comes from these projects or tutorials. All materials are provided for free private and public use.
Commercial use prohibited without prior written permission from www.electronics-tutorials.com.