1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electric field help needed

  1. Sep 14, 2005 #1
    I apologise for any spelling errors or terms missnamed since I am swedish and this course Im reading is only swedish books and terms. But I think I have gotten the translations right. Also my first try with latex.

    I have a non conducting sphere with the radius R and the volume charge density

    [tex] \rho (r) = \rho_o (1- \frac{r}{R} [/tex] when 0<r<R
    and [tex] \rho(r) = 0 [/tex] when r>R
    where [tex] \rho_0 [/tex] is a positive constant.

    I want to calculate the field E(r) for 0<r<R and R<r and I want to use this forumla

    E = \int \frac{dQ \hat{r}}{4 \pi \epsilon r^2}

    This is how I do it

    E = \frac{\rho}{4 \pi \epsilon_0 } \int_{0}^{r} (1-\frac{r}{R}) sin\theta d\theta dr d\phi

    I get that to [tex]\bar{E}= \frac{\rho_o}{\epsilon_0} (r- \frac{r^2}{2R}) \hat{r} [/tex]

    is that a correct answere for 0<r<R??

    gonna post this now and se if I got the latex right
    Last edited: Sep 14, 2005
  2. jcsd
  3. Sep 14, 2005 #2
    if I use gauss

    \oint Eds = \frac{{Q_e_n_c_l}}{{\epsilon_o}}

    with [tex] Q_e_n_c_l = \int_{0}^{r} \rho_0(1 - \frac{r}{R}) r^2 \sin \Theta dr d \Theta d \Phi = \rho_0 4\Pi (\frac{r^3}{3} - \frac{r^4}{4R}) [/tex]

    I get as answere
    [tex] \overline{E} = \frac{\rho_o}{\epsilon_0} ( \frac{r}{3} - \frac{r^2}{4R}) \hat{r} [/tex]

    why do I get different answeres. What equation do I implement wrong(or do I do them both wrong)?

    seems like the latex wont work :confused:
    Last edited: Sep 14, 2005
  4. Sep 14, 2005 #3
    might want to fix your tex tags. put the tags on the same line as the code
  5. Sep 14, 2005 #4
    found my error. I used capitals by misstake in the [ /tex ] :blushing:
    Last edited: Sep 14, 2005
  6. Sep 15, 2005 #5
    I solved it today fortunaly :)
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Electric field help needed