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Homework Help: Electric field question.

  1. Jun 22, 2005 #1
    Hum. Confused.

    Two charges -4.0mC and -5.0mC are separated by a distance of 20cm. What is the electric field halfway between the charges?

    Coulombe's law only tells me the force on a particle next to another one. I don't know the formula for calculating an electric field, let alone what it equals halfway between two charged particles. any help is appreciated.
  2. jcsd
  3. Jun 22, 2005 #2
    Look guys, this isnt homework and im not asking anyone to do it for me. Its just in the review for a huge test (the final) tomorrow and i cant remember back to when we studied it. If someone could even just give me the equation so i could solve it myself id be most grateful.
  4. Jun 22, 2005 #3
    Electric field = Force / Charge
  5. Jun 23, 2005 #4
    The electric field at distance r, in this case 0.1 m, from charge Q is:

    Q / (4pi*E0*r^2)

    where E0 is the permitivity of free space. In your case, you will need to find this for both values of Q and add them together.
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