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Old 6th January 2006, 10:16 PM
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Default Written capacitance units

The Greek letter mu (like a u but with a tail starting the letter) is the correct symbol for micro which means millionth.

Mu isn't available on many keyboards so m is sometimes used instead. This can be confusing though as m is used in the SI system for milli, which is a thousandth, and there is a capacitance unit of a millifarad although it's not often used.

In older circuits you often see mmf which is not m for milli either but means million millionths of a farad, or pF picofarads as we know them now.

In electronics it is safer to use the keyboard letter u for the Greek letter mu as it looks similar and can`t be confused with any other notation.

The units are,

1 Farad (F) =

1000 milli Farad (mF - not generally used) =

1000 000 micro Farad (uF) =

1000 000 000 nano Farad (nF) =

1000 000 000 000 pico Farad (pF - old mmF)

Some capacitor values may be marked in alternative ways such as a number followed by K being used to show thousands of pF (= number of nF).

Most formulae use the full Farad, so convert the value for calculations. The units relate by thousands/thousandths so remembering their names, including milliFarads, is useful for this.

Example,

10,000pF = 10nF = .01uF = .00001mF = .00000001F

All we do is move the decimal point 3 places at a time. If doing a calculation (i.e. to find the impedance of the capacitor at a known frequency) the last value, expressed in Farads, would be the one to use

Last edited by John Caswell; 1st November 2013 at 04:47 PM.
 

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