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Emf, current, electric fields...what direction is everything moving?

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dak246
#1
Mar4-06, 04:20 PM
P: 30
This is a very simple question but I can't seem to figure out the actual direction that things are moving in a simple circuit. Suppose you have a simple circuit consisting of a battery and a resistor: The electrons inside the battery are moving via work done by the battery towards the positive terminal from the negative terminal so that the "positive" terminal of higher potential is actually negatively charged...is that right? The drifting electrons in the circuit then move from the positive terminal of the battery (with the higher potential) to the negative terminal of the battery...correct? Also I assume that the electric field set up in the circuit is directed towards the positive terminal of the battery since it would be directed away from the postive charge (or less negative charge)of the batteries negative terminal. Finally, how can one think of the electric field inside the battery? Sorry for such a simple question but with all these signs and direction arrows its hard to keep track of whats actually going on...thanks in advance for any help.
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Chi Meson
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Mar4-06, 04:38 PM
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No. The positively charged terminal is positive. The difference in charge creates the "potential difference" (emf)which in turn sets up an electric field within the wire. THe field "points" from the positive to the negative terminal. The "pointing" of the field is by definition only.
The field causes charged particles to feel a force. THe particles that move are called electrons, which are negatively charged, and therefore feel a force that points opposite the direction of the electric field.

Within the battery, electrons flow from the positive to the negative terminal, so within the battery, the net field must point from positive to negative.
dak246
#3
Mar4-06, 05:20 PM
P: 30
Ok that cleared it up for me a bit...but let me sure I got it. So when its mentioned that "positive" charge carriers are moved from the negative to positve terminals inside a battery, one can interpret this as electrons moving from the postive terminal to the negative terminal inside the battery. And inside the circuit, the field "points" away from the postive end of the battery (I take it because of the arbitrary test charge thing) and thus electrons are moving toward the positive end, opposite the "current arrows" that point towards the negative terminal which symbolize postive charge carriers.

Chi Meson
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Mar4-06, 07:29 PM
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Emf, current, electric fields...what direction is everything moving?

Quote Quote by dak246
Ok that cleared it up for me a bit...but let me sure I got it. So when its mentioned that "positive" charge carriers are moved from the negative to positve terminals inside a battery, one can interpret this as electrons moving from the postive terminal to the negative terminal inside the battery. And inside the circuit, the field "points" away from the postive end of the battery (I take it because of the arbitrary test charge thing) and thus electrons are moving toward the positive end, opposite the "current arrows" that point towards the negative terminal which symbolize postive charge carriers.
That's right.

In wet cell batteries, there are actually positive ions that flow to the positive terminal. In solid conductors, only electrons move, and they go "backwards." It's all Ben Franklin's fault.
dak246
#5
Mar4-06, 09:01 PM
P: 30
Quote Quote by Chi Meson
That's right.

In wet cell batteries, there are actually positive ions that flow to the positive terminal. In solid conductors, only electrons move, and they go "backwards." It's all Ben Franklin's fault.
Thanks alot for clearing all this up for me.


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