Does U=qV or -qV? I notice my textbook uses qV but

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Discussion Overview

The discussion revolves around the expression for electric potential energy, specifically whether it should be represented as U=qV or U=-qV. Participants explore the implications of these formulations in the context of electric potential and the forces acting on charges.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant notes that their textbook uses U=qV, while an online lecturer uses U=-qV, leading to confusion about which is the correct convention.
  • Another participant asserts that U=qV is correct and emphasizes the distinction between potential energy and force, stating that the force on a positive charge moves in the direction of decreasing potential.
  • A later reply seeks clarification on the relationship between U=qV and the force equation F=qE, questioning if U would be negative when a charge moves in the direction of the force.
  • Another participant agrees with the previous assertion but suggests that the explanation could be clearer, indicating that the change in U=qV would be negative if the charge moves in the direction of the force.

Areas of Agreement / Disagreement

Participants express differing views on the correct formulation of electric potential energy, with some supporting U=qV and others considering U=-qV as more conceptually understandable. The discussion remains unresolved regarding which expression is the standard convention.

Contextual Notes

There are unresolved assumptions regarding the definitions of potential energy and the role of the negative sign in the context of electric fields and forces.

belledona
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Hi I have a question about electric potential! Since the negative sign isn't used in U=qV, and a-b is used for subscripts, then that takes care of the negative. But what about using U=-qV? An online lecturer uses U=-qV, while my textbook uses U=qV and then uses -qV to explain the force used to move a charge AGAINST the electric field. I'm wondering if qV or -qV is convention, because -qV is easier for me to understand conceptually but I lose the negative sign sometimes during problems...

Thank you!
 
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U=qV is correct.

The force is different, so don’t get confused about that. The force on a positive charge points in the direction of decreasing potential.
 
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Dale said:
positive

Dale said:
U=qV is correct.

The force is different, so don’t get confused about that. The force on a positive charge points in the direction of decreasing potential.
hi, thanks for your answer! so U=qV would only be negative if F=qE --> q=F/E (force is negative) here?
 
Essentially yes, but the way you wrote it is a bit sloppy. To make it correct you would need to say:

The change in U=qV would be negative if q moves in the direction of F=qE here?
 

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