Using e in a Formula: Electric Potential

[hardwork]

When using e (for electron) in a formula, do you use +1.6x10^-19 C or -1.6x10^-19 C?

For example:

http://i44.tinypic.com/25g9te8.jpg

An electron moved from c to a. How much work is done by the electric force?

Electric Potential
Point a = 6.2x10^5 V
Point c = -7.5x10^4 V

Work = (-1.6x10^-19 C) (Va - Vc) = -1.1x10^-13
-W(electric force) = +1.1 x 10^-13

OR

Work = (1.6x10^-19 C) (Va - Vc) = 1.1x10^-13
-W(electric force) = -1.1 x 10^-13

 

[LowlyPion]

Welcome to PF.

Electron carries a negative charge.

 

[rl.bhat]

According to the definition of the potential difference between the two points, it is the work done on the positive charge to move it against the electric force.
So the magnitude of the work is the same. Only difference is whether it is on the charge or by the charge.