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Homework Help: Electric field strength

  1. Jun 12, 2014 #1
    Physics Problem , please help I'm writing a test tomorrow and want to know if I'm right.
    The Question :

    Two point charges Q1 and Q2 are spaced 3m apart.

    Q1's charge = 14C
    Q2's charge = +20 C

    *Q1 -------(3meters)------- *Q2 ----(2meters)---- *P

    Calculate the net electric field at point P, 2m right from where Q2 is situated?

    My Calculations :

    Q1 on P = -5.04 x10^9
    Q2 on P = 4.5 x10^10

    Final answer = Net : 3.996x10^10

    Formula used:

    E = (k*Q)/r^2
  2. jcsd
  3. Jun 12, 2014 #2


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    Gold Member
    2017 Award

    Hello, Burger. Welcome to PF!

    Did you forget to include the sign of Q1 when you stated Q1 = 14 C?

    It is important to always include units with your answers.

    Just to be sure that you have a full understanding, what is the interpretation of the negative sign for your answer for the electric field of Q1 at P?

    Finally, electric field is a vector. So, it has a magnitude and a direction. Therefore, your final answer for the field at P should include both a magnitude and a direction. The direction should be clearly stated and not left to the reader to interpret.

    Otherwise, your numbers look good! (You're getting a very large answer because a Coulomb is a huge amount of static charge.)
  4. Jun 12, 2014 #3
    Q1's charge = -14 C

    Thanks for the help! Will ace the Test hopefully. I must just remember to include the direction the N•C^-1
  5. Jun 12, 2014 #4


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    OK. Good luck with the test!
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