# Homework Help: Units of Coulomb, trouble understanding the question

1. Jul 23, 2011

### JFonseka

1. The problem statement, all variables and given/known data
Two charges, q1 = 4.9 e C and q2 = -3.6 e C are located 105nm apart, what is the size of the force between the two charges?

2. Relevant equations

F=kqq/r^2

3. The attempt at a solution

I did it according to the formula and I got the answer wrong, so I checked it using an online force calculator between charges, and it gave the same answer I initially got. I looked up what e C is, thinking maybe it's indicating something smaller than 1 C, and couldn't really find a graduation for that, what am I doing wrong? Is it meant to be multiplied by 1.6 x 10^-19?

2. Jul 23, 2011

### mathfeel

Actually $q_1 = 4.9 e C$ is somewhat incorrect. $e = 1.6\times10^{-19}C$ is the elementary charge and already contain the unit Coulomb. So it is as if $q_1$ has unit Coulomb-Coulomb.

3. Jul 23, 2011

### JFonseka

So does this mean that I have to multiply 4.9 by 1.6x10^-19?

4. Jul 23, 2011

### JFonseka

Nvm, problem(s) solved.