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 Magnetism

  1. Mar 16, 2014 #1
    I need some help figuring #2 problem out.

    The problem statement, all variables and given/known data

    1. two charges of 6 microcoulombs and 10 microcoulombs are 10cm apart. Calculate their force of repulsion. Calculate the electric field midway between them.



    2. For the charges in question 1 calculate the potential midway between them. Calculate the work to bring an electron from far away to midway between them.



    So for the first question I used F= k |q1||q2|/r^2 for the second part of the first question i did E = k |q|/r^2

    i calculated that the force would be 53.94N
    As for the electric midway I calculate it to 3.6 x 10^6 N/c Although im not sure if i was supposed to add or subtract E1 and E2. So what i did is that i subtracted. But im not entirely sure if that is my correct answer


    My work:
    E1 = 8.99x 10^9 N*m^2/c^2 x |6 x10^-6 C|/(0.1m)^2

    E1 = 5.39 x 10^6 N/c is my answer for E1

    E2 = 8.99 x 10^9 N*m^2/c^2 x |10 x 10^-6C|/(0.1m)^2

    E2 = 8.99 x 10 ^6 N/C

    Then i did E = 8.99 x 10^6 N/C - 5.39 X 10^6 N/C
    And I got 3.6 x 10^6 N/C however like i said before im not exactly sure if this was the correct approach to get the electric field midway


    For the second question
    I used this equation (U= k (q0)(q)/r ---> k being 8.99 x10^9n.m^2/c^2 for part of the 1st question in question 2 that asks for potential midway and got an answer of U= 10.78 N M

    however when they asked me for the work in question two i assumed I should have used -W=q0Ed
    but i don't know what numbers I would use for this equation. Would the correct way of going about it be
    doing -W=(1.60 x 10^-19C)(8.99 x 10^6 N/C - 5.39 X 10^6 N/C)(0.1m) or is this wrong?

    IF someone could please point me in the right direction and check if I've done these steps correctly it would be helpful. Thank you in advance.
     
    Last edited: Mar 16, 2014
  2. jcsd
  3. Mar 16, 2014 #2
    Hey there!

    Yep. That's right.

    You're almost correct here - I'd say to take a look at your value for r again. As in, what are you measuring r to be again?


    As for both parts of the second question:

    The formula for U is for electrical potential energy, not the potential. But - there's a relationship between the two quantities, as well as one between W and U. Once you find those out, you're good to go.
     
  4. Mar 16, 2014 #3
    You're almost correct here - I'd say to take a look at your value for r again. As in, what are you measuring r to be again?

    Well I take the idea it's 10cm i converted that into 0.1m. Um Im guessing since they are asking me to calculate the electron from far away to midway. I would only take into account half of the original distance right?
     
  5. Mar 16, 2014 #4
    Well I take the idea it's 10cm i converted that into 0.1m. Um Im guessing since they are asking me to calculate the electron from far away to midway. I would only take into account half of the original distance right?
     
  6. Mar 16, 2014 #5
    In regards to the Electric field problem, the question asks for the electric field at the midway point between the two charges. A radius of 10 cm here would imply that the point in question is at either charge.

    With respect to the Potential Energy, yes. To be more technical, it's ΔU = Uf - U0, and if you use an r = ∞ for Uf, that expression becomes just -U0.
     
  7. Mar 17, 2014 #6
    Sorry for the late reply and thank you very much i finally understood it :D.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Electric Magnetism
Loading...