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Homework Help: Electric Field Vector for point charge

  1. Jan 15, 2008 #1
    b]1. The problem statement, all variables and given/known data[/b]

    Point charge q1= -5.00 is at the origin and point charge q2= +3.00 is on the -x axis at x= 3.00 cm. Point P is on the y-axis at y= 4.00 cm .

    Calculate the electric fields E1 and E2 at point P due to the charges q1 and q2. Express your results in terms of unit vectors (see example 21.6 in the textbook).

    Express your answer in terms of the unit vectors [tex]\hat{i}[/tex] , [tex]\hat{j}[/tex]. E

    2. Relevant equations

    r = [tex]\sqrt{x^2 + y^2}[/tex]

    [tex]\hat{r}[/tex] = ([tex]\vec{r}[/tex]/r =x[tex]\hat{i}[/tex] + y[tex]\hat{j}[/tex]) / r
    [tex]\vec{E}[/tex] = k * q/r^2 8 [tex]\hat{r}[/tex]

    3. The attempt at a solution

    So E1 will be the vector from q1 to point P
    r = [tex]\sqrt{0^2 + .04^2}[/tex] = .04 m

    [tex]\hat{r}[/tex] = (0[tex]\hat{i}[/tex] + .04[tex]\hat{j}[/tex])/.04 = 0[tex]\hat{i}[/tex] + 1[tex]\hat{j}[/tex]

    E1 = (8.98 e 9) * (-5.00 e -9) / .04^2 (0[tex]\hat{i}[/tex] + 1[tex]\hat{j}[/tex])
    = 0[tex]\hat{i}[/tex] - 2.81 e 4[tex]\hat{j}[/tex]

    i did the exact same steps to find E2 and
    E2 = 6.47 e 2[tex]\hat{i}[/tex] + 8.62 e 2[tex]\hat{j}[/tex]

    am i doing something wrong accordin to the steps i used because my answers are wrong. and i even followed the way the steps were in the book.
    i dont get it :confused:
  2. jcsd
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