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Homework Help: 3 point charges in the x direction

  1. Mar 14, 2006 #1
    Here is the problem:
    Three point charges are aligned along the x-axis as shown below. Find the electric field at the position x = +2.0m, y=0.
    ..............................y
    ..............................|
    --------|<--.50m --->|<--------------.80m-------->|
    --------0------------0-----------------------------0--------- X
    ........-4.0nC.............|5.0nC..............................3.0nC
    ..............................|

    So, I figured that I have to add up the E along the x axis and that should give me my answer. But, I'm not sure what to do with the numbers when they are already an Electrical Field... -4.nC isn't the charge, so, don't I need to find the q (or charge) first? then put it in the form kq/r^2??

    The only way I can come up with the answer is wrong... total E = 4,
    EA = 4 nC X 2m = 8 nC/m. 3 Charges times 8 nC/m = 24 nC... But that was simply a coincidence, I'm sure. 24 nC is the right answer, just need help getting there.:eek:

    Thank you in advance for your help and patience.
     
  2. jcsd
  3. Mar 14, 2006 #2

    eep

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    Are you sure? Those are units of charge, not of the electric field.
     
  4. Mar 14, 2006 #3

    Galileo

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    Science Advisor
    Homework Helper

    Why isn't -4.0 nC a charge? Isn't nC a nano-Coulomb? So it has units charge. The electric field has units N/C or V/m. So how can 24 nC be the right answer when it has the wrong units?
     
  5. Mar 14, 2006 #4
    Unfortunately, the book says that 24nC is the answer. Its been wrong before, but not very often.

    and about the nC, I was thinking it was Newton per Couloumb. Didn't even consider a nano couloumb... I will run with that. Thankyou
     
    Last edited: Mar 14, 2006
  6. Mar 14, 2006 #5

    eep

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    The units are definately wrong if that's supposed to be an electric field...
     
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