Calculating Net Electric Field Strength at Point A

[Coco12]

Homework Statement

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

Homework Equations

E=kq/d^2

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..

 

[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. ]

 

[Coco12]

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. ]

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

 

[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.

 

[HalfLostAndSearching]

As a scientist, it is important to understand the concept of vector addition when calculating net electric field strength. In this case, the direction of the electric field is taken into account when adding the individual electric fields of the two charges. Since the electric field due to the 3.7*10^7 charge is pointing to the left, it is considered a negative value. However, the electric field due to the 7.71*10^6 charge is pointing to the right, which is considered a positive value. When adding these two vectors, the negative value and the positive value cancel each other out, resulting in a net electric field strength of 4.5*10^7 N/C directed to the right at point A. It is important to remember that when adding vectors, the direction and magnitude must both be taken into account.