The electrical charge on a single proton, equal to approx. 1.602 × 10−19 coulombs; symbol e or qe.
The value of the elementary charge was first calculated in 1909 by Robert Millikan and Harvey Fletcher by measuring the equal but opposite charge on the electron. Although there are particles having a smaller electrical charge than the proton (or electron), these cannot exist independently of other particles.
Early 20th century; earliest use found in The Physical Review.