# E fields from a charged rod

1. Nov 21, 2006

### charlotty

ive already posted this is another bit of the forums, and only just noticed the Electronic Engineering section!!

My boyfriend is doing a dgree in electronic engineering and is studying fields and devices at the moment and is really stuck so i was wondering if anyone could help!!!

His notes say "the total e field is the vector sum over all the N charges. If we line up our axes so that the charges are on the x axis then we get..."
a really long equation. (i would write it here, but theres no way to get all the equations symbols!)

THe equation has a x' in it, and he has no idea what the notation means.

im probably not making any sense to anyone, but i just wanted to see if i could help him (im studying for a law degree so this is all spanish to me!)

thanks so much,

charlotty

2. Nov 21, 2006

Actually there is a way to get all of those crazy symbols. Here is an example,

$$\oint_S \vec E \cdot d\vec S = \frac{Q_{enc}}{\epsilon_0}$$

There is a lot of symmetry in your problem, how are you going about solving it?

EDIT:
I just noticed that you did not say an infinite rod. So my symmetry comment above is misleading. Instead you will need to sum of differential elements of voltage or electric fields.

$$V = \frac{1}{4 \pi \epsilon_0} \int_{V'} \frac{\rho}{R} \, dv'$$

Last edited: Nov 22, 2006
3. Nov 21, 2006

Also, the notation $x'$ is usually used to denote a variable corresponding to a source point. IE, the vector $\vec r'$ would point to the location of a point charge.