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!

Four charges equal in magnitude form a square

  1. Jun 7, 2015 #1
    1. The problem statement, all variables and given/known data

    Four charges equal in magnitude of 20.0 microC are placed on the four corners of a square with side length 0.180m. Determine the electric field at the centre of the square.

    (-q) ---------- (+q)
    l l
    l l
    l l
    (+q)----------(+q)

    1 --------------- 2

    3-----------------4

    Formatting messes up the square but you get the point.

    2. Relevant equations

    ɛ = kq / r
    ɛ = delta V / r

    3. The attempt at a solution

    I tried just adding up the combinations of each charge after calculating ɛ = kq / r for each. I didn't feel confident this was the correct way to do it, but no answer or solution was given.

    ɛ1 = k(-0.00002) / 0.180 = -1.00 x 10^6
    ɛ2&3&4 = k(0.00002) / 0.180 = 1.00 x 10^6

    ɛtotal = ɛ1 + ɛ2 + ɛ3 +ɛ4
    = -1.0 x 10^6 + 3(1.0 x 10^6)
    = 2.0 x 10^6
     
    Last edited: Jun 7, 2015
  2. jcsd
  3. Jun 7, 2015 #2

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Please show your work in more detail. There is no way we can tell if you did it right or wrong based on your post.
     
  4. Jun 7, 2015 #3
    Updated my solution to show my full work.
     
  5. Jun 7, 2015 #4

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    First of all, the distance from the charges to the center is not 0.18 m.

    Second, the electric field is a vector. You cannot simply add the magnitudes of the fields from each charge. You need to add the field vectors as a vector addition, i.e., using both magnitude and direction.
     
  6. Jun 7, 2015 #5
    Right.

    So I found the length to the centre from each corner to be 0.127m.

    So if I were to add them as vectors would charge 2 and 3 cancel each other out, and I would be left to add charges 1 and 4 together since they are opposite charges?
     
  7. Jun 7, 2015 #6

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Correct.
     
  8. Jun 7, 2015 #7
    Awesome thanks.

    One last thing, is there a rule for determining which way the electric field vector is going? Like will it be towards 1 (-q) or 4 (+q)?
     
  9. Jun 7, 2015 #8

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    The field is pointing in the direction in which the force on a positive test charge at the given position would point. Thus, the field from a negative charge points towards it (the negative charge) and the field of a positive charge away from it (the positive charge).
     
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: Four charges equal in magnitude form a square
Loading...