Current in DC Circuits: Positive & Negative

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Discussion Overview

The discussion revolves around the concept of current in direct current (DC) circuits, specifically addressing when current is considered positive or negative. Participants explore the definitions and implications of current direction in relation to charge flow, including electrons and protons, and the conventional current model.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that the designation of current as positive or negative depends on the chosen direction of measurement.
  • One participant describes a scenario with electrons flowing from the negative to the positive terminal of a battery and questions whether this results in a positive or negative current value.
  • Another participant raises a similar scenario involving protons moving from the positive to the negative terminal, seeking clarification on the current's sign in this case.
  • It is mentioned that conventional current is defined as the direction in which positive charge carriers would flow, which is opposite to the flow of electrons.
  • Participants discuss that if the flow of electrons is defined as the positive direction, the current would be negative since conventional current flows in the opposite direction.

Areas of Agreement / Disagreement

Participants express uncertainty and seek clarification on the definitions and implications of current direction. There is no consensus on a definitive answer regarding when current is positive or negative, as it appears to depend on the chosen reference direction.

Contextual Notes

Participants highlight the importance of defining the positive direction when discussing current, indicating that the sign of the current can vary based on this choice. There are unresolved questions regarding specific examples and the implications of different charge carriers.

streetfightr4
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In a direct current circuit, when is a current negative and when is it positive.
 
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streetfightr4 said:
In a direct circuit, when is a current negative and when is it positive.
Not sure what you mean. Generally, positive or negative is with respect to some direction.
 
Doc Al said:
Not sure what you mean. Generally, positive or negative is with respect to some direction.

lets say I have a direct current circuit and i have a battery with + and - terminals with a wire between them and i have electrons flowing from the negative terminal to the positive terminal through the wire. Is the current in this case a positive value or a negative value?

and now let's say that this time I have protons going from the positive to the negative through the wire instead. Is the current value in this case positive or negative?
 
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streetfightr4 said:
lets say I have a direct current circuit and i have a battery with + and - terminals with a wire between them and i have electrons flowing from the negative terminal to the positive terminal through the wire. Is the current in this case a positive value or a negative value?

and now let's say that this time I have protons going from the positive to the negative through the wire instead. Is the current value in this case positive or negative?
Sorry, but I don't understand what you're asking. The current has a direction, as you indicated. (Conventional current is the direction in which positive charge carriers would flow.) Whether you call the current positive or negative depends on what you are taking as the positive direction.

Do you have a specific example of a problem you are asked to solve that requires the sign of the current?
 
Current is positive when measured in the direction in which it is flowing. It's negative when it's measured in the opposite direction.
 
Doc Al said:
Sorry, but I don't understand what you're asking. The current has a direction, as you indicated. (Conventional current is the direction in which positive charge carriers would flow.) Whether you call the current positive or negative depends on what you are taking as the positive direction.

Do you have a specific example of a problem you are asked to solve that requires the sign of the current?

sorry I am not very good at this but let's say I have a battery with + and - terminals and I put a wire between them. So now I am guessing the electrons flow from the - terminal to the + terminal through the wire. Now let's say I choose the the direction of the flow of the electrons as the positive direction (from - terminal to + terminal) , what is the sign of the current?
 
streetfightr4 said:
sorry I am not very good at this but let's say I have a battery with + and - terminals and I put a wire between them. So now I am guessing the electrons flow from the - terminal to the + terminal through the wire. Now let's say I choose the the direction of the flow of the electrons as the positive direction (from - terminal to + terminal) , what is the sign of the current?
Again, the conventional current moves opposite to the direction that the electrons move. That current moves from + to -. Since you defined that as the negative direction, the current will be negative. But it depends on what real question you are trying to answer with the 'sign' of the current.

As PhaseShifter stated, if you are moving from A to B, then that is the nominal positive direction. If the current moves in that direction, consider it positive. (Of course, if you go from B to A, that current will be negative.)
 

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