# AC/DC vs conventional/electron flow current

Conventional current is from positive to negative and electron flow is from negative to positive. If we go with conventional current sign, would it be right to say DC current is always as per the conventional current and AC current switches between conventional and actual electron flow? Or these two directions are completely different and I am using it incorrectly.

• From what I understand you flip the positive and negative terminals(back and forth) in AC so we still use "conventional current" It's just that the entire +/- sides have now swapped. – Brad S Jan 4 at 13:24

## 4 Answers

Both DC and AC can be described from the viewpoint of the conventional current direction. The only difference is that for AC the direction changes all the time. But as it changes, so does the electron flow direction change. So is still opposite to the conventional current.

In fact it is the polarity of what drives the current, that changes all the time.

• In DC, you have a fixed polarity. Like attaching a battery. Positive potential at one end, let's call it A, negative at the other, let's call it B. Current flows from positive to negative potential, so from A to B. This is the conventional definition. For metallic wires and component, electrons are charge-carriers and they move oppositely, from B to A.

• In AC, you have a varying polarity. Like constantly flipping the battery over.

• You start out with positive potential at A and negative at B, in which case current flows from positive to negative, from A to B. Electrons flow oppositely, from B to A.
• But in the next instant you flip the polarity and have negative at A and positive at B. But current still flows from positive to negative as always, so from B to A. And electrons flow from A to B now now that the polarity flipped. Everything flipped when the polarity flipped. The conventional current direction is still and always opposite to the electron flow direction, because they both flip.

And it will always be like this. Because conventional current is defined as if the current was a positive charge-carrier. So it will always be opposite to the electron flow direction, because that is based on the negative electron charge-carrier.

No, that's not true. Conventional current is always from possitive to negative, whereas the electron flow is from negative to possitive, always against current.

In short:

• Possitive charges move in the same direction as $$I$$.
• Negative charges move in the opposite direction of $$I$$.

In circuits you have electrons, and they always go "against" the current vector.

In AC current, the $$I$$ arrow is changing direction. The electron flux is also changing direction, with the same ferquency, but the changes are the opopsite, so that you always have

$$I\rightarrow; \qquad \Phi_e \leftarrow$$

or

$$I\leftarrow; \qquad \Phi_e \rightarrow$$

Where $$I$$ is the intensity of current and $$\Phi_e$$ is the electron flux.

If we go with conventional current sign, would it be right to say DC current is always as per the conventional current and AC current switches between conventional and actual electron flow?

Not quite. For currents in metal the charge carriers are negative, $$\rho<0$$. Since the current density is $$\mathbf J= \rho \mathbf v$$ that means that the current is always in the opposite direction as $$\mathbf v$$.

In AC circuits when the charges are moving in the positive direction then the current is in the negative direction, and when the charges are moving in the negative direction then the current is in the positive direction. The conventional current is always opposite the direction of the electron movement.

Note, in electrolytes and some other situations the charge carriers may be positive. In those cases the current would be in the same direction as the motion of the charge carriers. You can even have charge carriers with both signs, in which case the current would consist of motion of positive charges in one direction and negative charges in the other. The electrical effects are almost* all based on the current so the sign of the charge carriers is usually irrelevant.

*The only exception that comes to mind is the Hall effect

Conventional current flows from positive terminal to negative terminal but after some discoveries it was found that in metals electrons are responsible for current so they said that electron flows from -ve terminal to +ve terminal but current still flows from positive to -ve terminal. Current is opposite to drifting of electrons. Now since DC always remains constant so DC current flows from positive terminal to negative terminal but in AC half of the time the current flows from positive terminal to negative terminal and even in the other half it flows from positive terminal to negative terminal because voltage also changes sinusoidally I.e. volatage i.e. terminals switch themselves. Current depends on volatge so if voltage flips so the direction of current. I hope I have made myself clear.

• Your answer is repeating what I already know and should have been clear from my question. Other answers are indeed resolving my query. – PagMax Jan 4 at 15:11