Symbols in Electricity Formulas
Why is the letter I used to represent current in formulas which deal
This is a good question. It may be because it was a letter next to
the letter j, since j is supposed to be the current per unit area and
thus I is the total current. It may also be that in French that I is
the abbreviation for something meaning current. I have looked at
one or two source books and cannot find anyone who knows. A book
on Science History may be a good source.
samuel p bowen
And why is current density "j"? Or why is charge "q"? "C" was already
used up for capacitance. Scientific notation can be kind of funny
sometimes. In fact, different areas of science can have totally
different notations for the same thing: because I is used so
much for current in electrical engineering, for example, the
standard notation everywhere else for complex numbers that
i is the square root of -1 is not used by them: instead they use j!
Basically, notation is set by convention, and in new areas of science
the notation can vary a lot from one scientific paper to another,
until it settles down after a few years. Sometimes something gets
two symbols instead of one, such as the J/psi particle, because different
groups never manage to agree on a common notation.
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Update: June 2012