What is a Capacitor?

A capacitor or condenser (previous name) is an electronic device that stores electrons.  It is similar to a battery in it's electron supplying capability but unlike one - in that, it does not generate or produce electrons.  Capacitors when charge up will block the flow of DC (Direct Current), where as AC (Alternating Current) can continually flow.  Capacitors are possibly the second most used electronic component next to resistors.  They have a variety of  uses; filtering in power supply circuits, frequency filtering in radio tuning circuits, charging cycles in timer circuits and filtering in high frequency circuits just to name a few.  The value of a capacitor is measured in farads.  A farad is a large unit however most capacitors used are measured  in microfarad (uf) or picofarads (pf).  1 Farad = 1,000,000 (uf )=1,000,000,000,000 (pf).  Some popular values are .1uf, 1uf, 2.2uf, 4.7uf, 10uf, 25uf, 35uf, 50uf, 100uf and 1000uf.  In addition to the capacitance rating they also have a voltage rating.  So putting a 16 volt 10uf capacitor across 50 volts would not be good for the capacitor.  The symbol for the capacitor on a schematic is shown below. 


There is much much more to be learned about capacitors such as how they are constructed, the different styles and types, how to calculate the charge on the internal plates and how to calculate the current flowing through it.

Additional reading and experimentation can be found in, Greg S. Carpenters Book, "Introduction to Basic Electronics Hands-On Mini Course". For more information on the book, Click Here!

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