# Arbitary or direction?

1. Jul 27, 2006

### momomo_mo

-----------> direction of E-field
the potential energy required to move +ions from infinity to that point is a positive value
But for -ions , the potential energy required is negative
Does the sign reveal the direction ,attractive force /repulsive force or any other arbitrary meaning or just because of the formula of potential energy and add a negative sign on it??
sign on it??

Last edited: Jul 27, 2006
2. Jul 27, 2006

### Andrew Mason

The convention for the direction of an electric field is the direction of the force that the field exerts on a positive charge.

We let the potential energy at infinity = 0. So if it requires work to move from infinity to a point, the potential energy is positive. This means the charge moves against a force. If it does work in moving from infinity to a point, the potential energy at that point is negative. This means that the charge moved in the direction of the electric force.

AM

3. Jul 27, 2006

### momomo_mo

That means it is the sign of direction?

4. Jul 30, 2006

### Claude Bile

No.

The the -ve sign in this context means that energy is being liberated (i.e. converted from potential energy into kinetic energy).

Knowledge of the potential at a single point does not allow you to infer direction of any sort, since it is a scalar quantity. Only if you have knowledge of the potential of the surrounding region, can you infer the gradient of the potential (i.e. the E-field) and thus all the forces that might act on the charge.

Claude.