Definition:Electric Charge/Polarity
Definition
The polarity of an electric charge can be one of $2$ types:
Positive Electric Charge
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.
Negative Electric Charge
A negative electric charge is an electric charge which is of the same polarity as the electric charge on an electron.
When it is necessary to assign a value to a negative electric charge, a $-$ (minus) sign is used, and the value assigned is a negative number.
Like Electric Charges
If $2$ electric charges are of the same polarity, they are referred to as being like (electric) charges.
Unlike Electric Charges
If $2$ electric charges are of different polarity, they are referred to as being unlike (electric) charges.
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
- 1990: I.S. Grant and W.R. Phillips: Electromagnetism (2nd ed.) ... (previous) ... (next): Chapter $1$: Force and energy in electrostatics: $1.1$ Electric Charge