# 3 point charges in the x direction

1. Mar 14, 2006

### Trista

Here is the problem:
Three point charges are aligned along the x-axis as shown below. Find the electric field at the position x = +2.0m, y=0.
..............................y
..............................|
--------|<--.50m --->|<--------------.80m-------->|
--------0------------0-----------------------------0--------- X
........-4.0nC.............|5.0nC..............................3.0nC
..............................|

So, I figured that I have to add up the E along the x axis and that should give me my answer. But, I'm not sure what to do with the numbers when they are already an Electrical Field... -4.nC isn't the charge, so, don't I need to find the q (or charge) first? then put it in the form kq/r^2??

The only way I can come up with the answer is wrong... total E = 4,
EA = 4 nC X 2m = 8 nC/m. 3 Charges times 8 nC/m = 24 nC... But that was simply a coincidence, I'm sure. 24 nC is the right answer, just need help getting there.

2. Mar 14, 2006

### eep

Are you sure? Those are units of charge, not of the electric field.

3. Mar 14, 2006

### Galileo

Why isn't -4.0 nC a charge? Isn't nC a nano-Coulomb? So it has units charge. The electric field has units N/C or V/m. So how can 24 nC be the right answer when it has the wrong units?

4. Mar 14, 2006

### Trista

Unfortunately, the book says that 24nC is the answer. Its been wrong before, but not very often.

and about the nC, I was thinking it was Newton per Couloumb. Didn't even consider a nano couloumb... I will run with that. Thankyou

Last edited: Mar 14, 2006
5. Mar 14, 2006

### eep

The units are definately wrong if that's supposed to be an electric field...