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Why is the letter I used to represent current in formulas which deal with electricity?

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.

Arthur Smith

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