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HELP Charge for an electric field

  1. Jul 2, 2008 #1
    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[tex]^{}2[/tex]
    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. jcsd
  3. Jul 2, 2008 #2

    Doc Al

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    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.
  4. Jul 2, 2008 #3
    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.
  5. Jul 2, 2008 #4

    Doc Al

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    Staff: Mentor

    Re: HELP!!! Charge for an electric field

    That equation isn't quite right. Instead of q, you should have [itex]\lambda[/itex], which is the charge per unit length. Read this: Electric Field of Line Charge.

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