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Homework Help: Electric Field Done Correctly?

  1. May 20, 2006 #1
    Two charges located along the x-axis, (-3*10^-6)C at the origin, and (6*10^-6)C at the point (2,0)

    What is the electric field at point -1,0?

    i did:

    Etotal = Eq1+Eq2

    =(k(q1)/r^2) + (k(q2)/(2-r)^2)
    =(-2.09*10^4) N/C

    Can someone please double check my calculations (i did it a few different ways and i always end up with a negative answer)? I plugged this into http://hyperphysics.phy-astr.gsu.edu/hbase/electric/e2p.html#c1 and for some reason their answer comes out positive. Which one is correct?
  2. jcsd
  3. May 20, 2006 #2

    Andrew Mason

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    Science Advisor
    Homework Helper

    The direction of the field is given by the direction of the force on a unit positive charge (ie. of +1C. ). [itex]\vec E = \vec F/q[/itex]. So, in this case the field is positive.

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