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!

Net electric field

  1. Jan 31, 2017 #1
    1. The problem statement, all variables and given/known data
    204.PNG

    2. Relevant equations
    Enetx=((kq1)/r^2 +^2) with the pos/neg of the coefficients being dependent on the position of the charges around the point

    3. The attempt at a solution
    As everything is one dimensional we can assume the j an k compnents of the electric field are 0
    Part a
    Ea= -(kq1)/r1^2+(kq2)/r2^2
    =-(8.99E9N)(3.7E-12C)/(.011m)^2+(8.99E9N)(-1.8E-12C)/(.022m)^2
    =-274.901 N/C+ -33.4339 N/C
    =-308.335 N/C

    This was incorrect and I am unsure of my mistake(s) and can only assume I would carry them over to the next two calculations
     
  2. jcsd
  3. Jan 31, 2017 #2

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    At A, the positive charge provides a negative component to the left and the negative charge provides a positive component to the right. You show two negative components. In short, you used the negative sign for the negative charge twice. It is probably easier to calculate the size of the component using positive values for all charges, figure out the direction of the field components from the diagram and add negative signs as needed.
     
  4. Jan 31, 2017 #3
    So you're saying I should use absolute values for both charges and hen decide direction when adding them together? So in this case it should have been -274.901+33.4339= -241.467 N/C?
     
  5. Jan 31, 2017 #4

    gneill

    User Avatar

    Staff: Mentor

    The signs of the charges along with the relative locations of the charges at the points of interest are mucking up your algebra. You either have to be very careful indeed to keep it all straight, or do the practical thing: First sketch in vectors for the field directions due to each charge at the points of interest. Then calculate the field magnitudes using absolute values for the charges. Write the algebra to incorporate direction based on the vector directions.


    Edit: Ah. I see that kuruman got there ahead of me! :smile:
     
  6. Jan 31, 2017 #5

    kuruman

    User Avatar
    Homework Helper
    Gold Member

    That's what I and @gneill are saying. Now you should be able to do the other two parts on your own. If not, you know where to go for help.
     
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: Net electric field
Loading...