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Homework Help: Electric potential, field and charge density problem check

  1. Nov 3, 2006 #1
    https://www.physicsforums.com/attachment.php?attachmentid=8198&stc=1&d=1162609042
    V – Electric potential

    I drew the picture of basically a rod with end points a and –a on the x axis with a point b that sits as well on the x positive axis.

    Assuming that is correct, I then am asked to find the electric field using my previous answer on the same point. I did not partially derrive with respect to y or z for the j and k vector components because the original potential equation has no y or z variables which means 0.
    https://www.physicsforums.com/attachment.php?attachmentid=8199&stc=1&d=1162609042

    Please let me know if the problems are worked out correctly.

    My next question is:

    Finding the volume charge density in spherical coordinates bounded by:

    https://www.physicsforums.com/attachment.php?attachmentid=8200&stc=1&d=1162609042

    The formula was given by my teacher as he told us to use that in spherical charge denisty problems. He proved it through a tedious triple integral which I was not able to completly copy down.
    The problem I am having is I thought I was correctly setting up the problem but when he was doing a similar problem today on magnetism i noticed his bounds resulted in having each integral with 2-3 parts. Like a to r plus r to 2a and etc. I do not understand.

    Please help me, if you guys need more details let me know.
     
  2. jcsd
  3. Nov 4, 2006 #2
    none of the links work for me.
     
  4. Nov 4, 2006 #3
    problem4.jpg

    problem5.jpg

    problem6.jpg
     
  5. Nov 4, 2006 #4
    all that work is mine so please help, I typed it up on microsoft equation editor 3.0 then pasted into paintbrush and uploaded it as an image.
     
  6. Nov 5, 2006 #5
    it's been a year since i've had e&m, but the first part looks ok. i'm kind of confused on the second part, because you're saying a is a variable. i thought a was a constant? i guess it doesn't really matter, because the general formula on the axis would be a---->x

    the second one requires different integrals because the charge distribution is different for different regions. so, you'd need an integral for each of those regions to accurately calclulate stuff. i.e. 0->a, a->2a -- each region has a different density. make sense?

    i had a rough time in e&m (even if i did get an A), so don't take my word as law.
     
  7. Nov 5, 2006 #6
    I see, let me try and get more clarification on the 3rd question. As for the second, a was constant but I have to differentiate with respect to x for the i component. Would I use the source point or field? I considered a to be the source which is technically x so i showed that by differentiating with respect to a.
     
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