# Electric Flux/Gauss' Law

1. Oct 2, 2007

### robbondo

1. The problem statement, all variables and given/known data

A point charge $$q_{1} = 4.15 \times 10^-6$$ is located on the x-axis at x = 1.80 m, and a second point charge $$q_{2} = -5.80 \times 10^-6$$ C is on the y-axis at y = 1.10 m. What is the total electric flux due to these two point charges through a spherical surface centered at the origin and with radius r = 1.45 m?
Take the permittivity of free space to be $$8.85 \times 10^{-12}\:{\rm C}^{2}/{\rm N \cdot m}^{2}.$$

2. Relevant equations

$$\phi_{E} = \frac{Q_{enclosed}}{\epsilon_{0}}$$

3. The attempt at a solution

I just divided the one charge inside the sphere by epsilon naught.

$$\frac{q_{2}}{\epsilon_{0}}$$

So I get, $$-6.55 \times 10^{5}$$

I'm sure I screwed something obvious up, any suggestions?

2. Oct 2, 2007

### dynamicsolo

Why are you sure you messed up? Show the calculation you made and also be sure to show your units.

3. Oct 2, 2007

### robbondo

I know I'm wrong because this hw's online and I got it wrong, and I loose points for every wrong answer suckily. Well the units for q were nanocoulombs which I changed to coulombs and then epsilon naught is $${\rm C}^{2}/{\rm N \cdot {m}}^{2}$$. So they cancel out do give $${\rm N \cdot m}^{2}/ \rm C}$$

Calculation was $$\frac{-5.8 \cdot 10^{-12}}{8.85 \cdot 10^{-12}}$$

crap... I used the wrong changing of units it $$1 \cdot 10^{-9}$$ coulombs per nanocoulombs... not -6.

Thanks solo.

4. Oct 2, 2007

### dynamicsolo

Well, that was easy on me... As a suggestion, when you present a problem in the forum, type it in exactly as it appeared originally. That would have made the SI prefix error easy to spot. Your method was correct!