Solving Cross Section Confusion: Adding Positive and Negative Ions

[arrozito]

Homework Statement

A fluorescent tube with 3 cm diameter has a flux of positive and negative ions in it. That flux is
2x10^18 electrons by second and 0.5x10^18 positive ions (with charge +e) by second. What’s the current
inside the tube?

(sol 0,4A)

Relevant Equations

I = dq/dt = (delta)q/(delta)t = q/t

ik that i have to add the positive and negative ions but the cross section (surface) confuses me how do i resolve this?

 

[BvU]

Hello arrozito, !

how do i resolve this

Well, since it does not occur in your relevant formula, perhaps you can forget about it ? Check what the answer is when you do (forget about it) !

Note: flux generally is per unit of area, but if the dimension of your given data doesn't have that, you may assume it is for the area of your device. Confusing, though !

Note 2: if you get a wrong answer of the right order of magnitude, consider the directions in which the charge carriers move: same or opposite ?