Definition:Electric Charge/Polarity/Positive
Definition
A positive electric charge is an electric charge which is of the same polarity as the electric charge on a proton.
When it is necessary to assign a value to a positive electric charge, a $+$ (plus) sign is used, and the value assigned is a positive number.
Convention
It appears at first glance that the definition of the polarity of an electric charge is both arbitrary and circular.
That is:
- a positive electric charge is the type of electric charge that can be found on a proton
while:
- a proton is defined as carrying a positive electric charge.
Early in the development of the theory of electrostatics, it was noticed that there were two types of electric charge.
What they were called was indeed arbitrary at that point in time; one type was called positive, and the other type was called negative.
When the proton and electron were discovered, the polarities of their electric charges were identified, and subsequently used to define the polarity of an arbitrary electric charge.
Hence the fact that a proton is positive and an electron is negative is simply the result of a convention.
Also see
Sources
- 1958: C.A. Coulson: Electricity (5th ed.) ... (previous) ... (next): Chapter $\text {I}$: Preliminary Survey: $\S 1$. Electrostatics
- 1990: I.S. Grant and W.R. Phillips: Electromagnetism (2nd ed.) ... (previous) ... (next): Chapter $1$: Force and energy in electrostatics: $1.1$ Electric Charge