# Homework Help: Point charge - magnitude calculations

1. Jan 18, 2010

### swimmer052005

1. The problem statement, all variables and given/known data
A 4.9-µC point charge is located at x = 1.1 m, y = 3.1 m, and a -3.9-µC point charge is located at x = 2.1 m, y = -1.9 m.

(a) Find the magnitude(inkN/C) and direction(in degrees) of the electric field at x = -3.2 m, y = 0.9 m.

(b) Find the magnitude(in N) and direction(in degrees) of the force on a proton at x = -3.2 m, y = 0.9 m

2. Relevant equations

3. The attempt at a solution
We haven't been taught this in class specifically, so i donn't know how to go about it. Help please!

2. Jan 18, 2010

### espen180

Use the equation for the Coloumb force:

$$\vec{F}=k_e \frac{q_1q_2}{r^2} \hat{r}$$

And the electric field

$$\vec{E}=\frac{\vec{F}}{q}=k_e\frac{q}{r^2}$$

and the superposition principle (E=E1+E2)