# Homework Help: Electric fields

1. Dec 11, 2013

### Coco12

1. The problem statement, all variables and given/known data

Find the net electric field strength at point A due to the combined electric fields of both charges.

2. Relevant equations

E=kq/d^2

3. The attempt at a solution
I know how to solve these type of problems however I'm just wondering how come in the net force line as you can see on my paper, they didn't use a -3.7*10^7 since it is going in the left direction.

The answer that was given was : 3.7*10^7+ 7.71*10^6 = 4.5*10^7 N/C

When I did electrostatic forces before that had charges in a line, you had to use negative when finding net force for charges that went to the left..

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2. Dec 11, 2013

### TSny

I agree with your line of thought . The magnitude of the net E field should be|-3.7*10^7+ 7.71*10^6|. The magnitudes of the individual fields should be subtracted because the individual electric field vectors point in opposite directions at point A.

[EDIT: To avoid giving people stiff necks, it would be nice to post your images so they are upright. ]

Last edited: Dec 11, 2013
3. Dec 11, 2013

### Coco12

So you are saying that the answer that was given was wrong?

4. Dec 11, 2013

### TSny

Yes. If one charge is positive, the other charge is negative, and the point A is located as shown in your diagram, then the given solution is wrong.