# HELP Charge for an electric field

1. Jul 2, 2008

### Aserap

HELP!!! Charge for an electric field

The electric field 0.375 {\rm m} from a very long uniform line of charge is 830 {\rm N/C}.

How much charge is contained in a section of the line of length 1.70 {\rm cm}?

I started doing this problem, and though it was the right approach, but then i continually get the wrong answer, i have two more tries left. this is what i did:

I used the equation:
E = q/ 4*pi*E0*r$$^{}2$$
and plugged in the electric field number given, with the known length of the line to get the charge of the particle... which came out to 1.30x10^-8 and from my own assumptions i thought regardless of what r is the charge should be the same, but it doesnt work. Can someone please help!!!

2. Jul 2, 2008

### Staff: Mentor

wrong formula

That formula describes the electric field from a point charge. You want a formula describing the field from a line charge.

3. Jul 2, 2008

### Aserap

Re: HELP!!! Charge for an electric field

i used this equation as the line charge
E= q/ 2*pi*Eo*r
at least this is the only one that i found, it not labeled in the book.
i used 830 for E and .017 for r and solved for q... i got 7.85x10^-10.
This isnt right. i was thinking could r be .375- .017 or something of that nature. i only have one more try to get this answer correct, and i feel so close but i keep getting wrong answers.

4. Jul 2, 2008

### Staff: Mentor

Re: HELP!!! Charge for an electric field

That equation isn't quite right. Instead of q, you should have $\lambda$, which is the charge per unit length. Read this: "http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/elecyl.html#c1" [Broken].

Once you figure out the charge per unit length, you can calculate the charge in that segment of the line.

Last edited by a moderator: Apr 23, 2017 at 1:57 PM