Use of I for Current
Date: Thursday, August 22, 2002
Why is the letter "I" used to represent current in Ohm's law?
I am not aware of any particular significance of the choice of "i" to
stand for current in Ohm's Law. Scientists choose symbols that may or may
not have any "extrinsic meaning".
Examples: 1. Both "E" and "V" are used to
stand for "voltage" in Ohm's Law.
2. Potential energy uses the symbols:
3. Both the letters "x,y,z" and "i,j,k" are used to label coordination axes.
The "H" is used to mean the Hamiltonian operator in physics, but the
enthalpy in thermodynamics. The point is, for many cases there is no
significance to the choice of symbols, but sometimes there is. Even in those
cases the "reason" is usually transparent, for example, the use of "e" for
the charge on the electron.
I do not know for a fact why, but I expect the word "current" was not always
used. It is possible that a term such as influx of charge was once used.
To use the first letter would cause problems because both charge and current
start with the same letter. "q" for charge and "I" for current may have
just been chosen because they look very different.
Dr. Ken Mellendorf
Illinois Central College
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