# Homework Help: Electric fields

1. Nov 14, 2005

### Pseudo Statistic

I have this question:

Positive charges are situated at 3 corners of a rectangle with charges q1, q2, and q3. Given each of their distances from the 4th corner of the rectangle, what is the electric field at the 4th corner?

Would it be the vector sum of the electric field of each of those at the 4th corner?
So, for q1, say it's r meters away, the field at that point would be:
E = q1/(4pi epsilon0 times r^2) ...
And then, knowing the angle at which it's pointed (relative to, say, the horizontal) I'd multiply it by the cosine of that angle and sine to end up with the x and y components, rinse and repeat for all of the others, add them all up (considering directions and signs) and then use Pythagoras' theorem, then finding the direction? Or am I thinking wrong?
Just want to know if I'm thinking of the right idea!
Thanks!

2. Nov 14, 2005

### Chi Meson

You are thinking correct. Do you think it couldn't possibly be so easy? Well it is.