Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Simple electric field problem

  1. Jan 12, 2008 #1
    Simple electric field problem....

    1. The problem statement, all variables and given/known data
    What magnitude charge creates a 4.17 N/C electric field at a point 9.78 m away?


    2. Relevant equations



    3. The attempt at a solution
    E = (k * Q) / r^2
    Q = (E * r^2) / K = 4.43 x 10^10 C
    Why isn't that right?
     
  2. jcsd
  3. Jan 12, 2008 #2

    hage567

    User Avatar
    Homework Helper

    Check your math. I don't get the same answer with the expression you used.
     
  4. Jan 12, 2008 #3
    oh shoot I was using K = 9 x 10^-9 because everything is in nC so thats what I did...thanks!!
     
  5. Jan 12, 2008 #4
    Is this question not asking the same thing?

    The electric field 4.1 cm from a small object points toward the object with a strength of 199400 N/C. What is the object's charge?

    q = 3.72 x 10^-8 C
     
  6. Jan 12, 2008 #5

    hage567

    User Avatar
    Homework Helper

    If the field is pointing towards the charge, what does that tell you about the charge?
     
  7. Jan 12, 2008 #6
    its negative
     
  8. Jan 12, 2008 #7

    hage567

    User Avatar
    Homework Helper

    Right. I don't see anything wrong with your calculation otherwise.
     
  9. Jan 12, 2008 #8
    thanks so much!!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook