# Homework Help: Electric Field Vector for point charge

1. Jan 15, 2008

### hteezy

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 $$\hat{i}$$ , $$\hat{j}$$. E

2. Relevant equations

r = $$\sqrt{x^2 + y^2}$$

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

3. The attempt at a solution

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

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

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

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

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