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

Charge problem

  1. Jun 7, 2005 #1
    two spheres have the same negative charge. Each sphere is held by a string .4m long.

    the spheres hang with a 40 degree andgle between them due to repulsion

    What is the electrical force experienced by each sphere?

    in order to get the answer I need d (which I can get using trig), Q1 and Q2.

    I'm stuck here... how do I get Q1 and Q2?
    any help is appreciated.
  2. jcsd
  3. Jun 7, 2005 #2


    User Avatar
    Homework Helper

    can you post an image? it'll help to imagine it correctly.
  4. Jun 7, 2005 #3


    User Avatar
    Science Advisor
    Homework Helper

    You need more information than you posted to solve this problem. What other forces beside electical repulsion are acting? There must be some or else the strings would be pointing in opposite directions, not 40 degrees apart.
  5. Jun 7, 2005 #4
    Ok i dont have the picture, but this should give you the idea. (the picture on the right)


    mass of each sphere = 5.0g
    length of each string = 40cm
    angle between the strings = 40 degrees (each sphere is 20 degrees from the vertical) due to repulsion

    the spheres each have the same negative charge.


    What is the magnitude of the electric force each sphere experiences?

    Attached Files:

  6. Jun 7, 2005 #5


    User Avatar
    Homework Helper
    Gold Member

    Draw the Free Body Force diagram for a sphere. What are the forces acting on the sphere? . At equilibirium all the forces are balanced. Equate the forces in the x and y directions for the sphere and you should be able to calculate the Force experienced due to the charges.
  7. Jun 8, 2005 #6
    ahh ok, thats pretty simple.

    the second part of the question is to find the values of each charge (they are equal but no value is given)

    I was trying to figure it out that way first.

    So I guess I draw the free body diagram first, find the electric force..

    then plug the electric force into Coulomb's Law equation to find Q.

    sound right? :biggrin:

  8. Jun 8, 2005 #7


    User Avatar
    Homework Helper
    Gold Member

    Yes, but make sure you use the correct value of distance between the two charges.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook