# Electric Field question - Why is this answer negative

• cros0
In summary, the conversation discusses the direction of electric fields and the sum of two E-fields at a point between two charges. The solution manual explains that the E-field at a negative charge points inward while the E-field at a positive charge points outward. This results in a negative direction on the horizontal axis. The person asking for clarification feels more at ease after understanding this concept.

#### cros0

Hello. The first image is the question, the second image is from the solutions manual. I don't understand why these answers are negative. Anyone have a clue?

cros0 said:
View attachment 101011
View attachment 101012

Hello. The first image is the question, the second image is from the solutions manual. I don't understand why these answers are negative. Anyone have a clue?
Sure. (and Welcome to the PF)

Electric field points from positive charges to negative charges. So the E-field at the first negative charge is pointing inward to that negative charge in all directions. The E-field at the positive charge is pointing away from it in all directions. They ask for the sum of the two E-fields at a point between them, so both components point to the left, which is the negative direction on the horizontal axis.

Does that help?

Seems reasonable enough, and I feel much better now. Thanks!

berkeman

## 1. Why do we use negative signs in electric field calculations?

The negative sign in electric field calculations represents the direction of the force exerted on a positive test charge. By convention, the direction of the electric field is taken to be the direction in which a positive test charge would move.

## 2. Does a negative electric field mean there is no electric field present?

No, a negative electric field simply means that the direction of the electric field is opposite to the direction in which a positive test charge would move. A negative electric field still indicates the presence of an electric field.

## 3. Can an electric field be both positive and negative?

Yes, an electric field can be both positive and negative depending on the location of the test charge. If the test charge is placed in a region where the electric field is directed towards the positive charge, the electric field will be positive. If the test charge is placed in a region where the electric field is directed towards the negative charge, the electric field will be negative.

## 4. Why is the electric field inside a conductor always zero?

Inside a conductor, the electric field is always zero because the free electrons in the conductor will rearrange themselves in such a way that the net electric field inside the conductor is canceled out. This is known as electrostatic equilibrium.

## 5. How does the distance between two charges affect the electric field?

The electric field is inversely proportional to the square of the distance between two charges. This means that as the distance between two charges increases, the electric field decreases. Similarly, as the distance decreases, the electric field increases.