Potential Energy +ions/-ions: Attraction/Repulsion?

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Discussion Overview

The discussion revolves around the potential energy associated with moving positive and negative ions in an electric field, specifically examining the implications of the signs of potential energy and their relation to attractive or repulsive forces. The scope includes conceptual understanding of electric fields and potential energy in the context of charged particles.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants note that the potential energy required to move positive ions from infinity to a point is positive, while for negative ions, it is negative.
  • One participant questions whether the sign of potential energy indicates direction, attractive or repulsive forces, or if it is merely a consequence of the formula used.
  • Another participant explains that the convention for electric field direction is based on the force exerted on a positive charge, suggesting that positive potential energy indicates work done against a force, while negative potential energy indicates work done in the direction of the electric force.
  • A different viewpoint argues that the negative sign indicates energy liberation, as potential energy converts to kinetic energy, and emphasizes that potential is a scalar quantity, which does not provide directional information without knowledge of the surrounding potential gradient.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the signs of potential energy and their implications for direction and force. No consensus is reached regarding the meaning of the signs in this context.

Contextual Notes

The discussion highlights the limitations of interpreting potential energy without considering the surrounding electric field and potential gradient, which are necessary for understanding directional forces.

momomo_mo
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-----------> 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??
 
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momomo_mo said:
-----------> 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??
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
 
That means it is the sign of direction?
 
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.
 

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