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Homework Help: Electric Fields- 2 Dimensions

  1. Jan 24, 2009 #1
    1. The problem statement, all variables and given/known data

    Use Coulomb's law to determine the magnitude and direction of the electric field at points A and B in Fig. 16-57 due to the two positive charges (Q = 4.0 µC) shown.


    3. The attempt at a solution

    Basically, I'm completely lost. I've applied Coulomb's law to find the magnitudes of the contributing electric fields.

    Can anyone help me solve this problem/ at least get started. Thanks so much, god bless.
  2. jcsd
  3. Jan 24, 2009 #2
    Apply Coulomb's law for each charge separately.
    Then use vector superposition once you find electric field for each charge.
  4. Jan 25, 2009 #3
    An electric field is a vector so it has a magnitude and a direction. Using Coulomb's Law gives an expression for E:

    [tex]\vec{E}=\frac{\vec{F}}{q}\mbox{ where q is a test charge}[/tex]

    [tex]\vec{F}=\frac{qQ\hat{r}}{4\pi \varepsilon_0 \ r^2}[/tex]

    [tex]\mbox{where }\hat{r}\mbox{ is the unit vector in the r direction}[/tex]


    [tex]\vec{E}=\frac{Q\hat{r}}{4\pi \varepsilon_0 \ r^2}[/tex]

    where r is the distance from the charge to the point in question. Resolve E into Ex and Ey using cosine and sine. Then add these resolved components to find the resultant components.
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