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# Confused about current, electron flow, resistance and temp. +rep available :) watch

1. Okay, so here's what I do know:
- Current flows from +ive to -ive, the opposite direction to which electrons flow.
- Current and resistance are inversely proportional to each other. So as I increases, R decreases.
=>SO does that mean resistance kinda encourages electron flow to limit the current?

One other thing I'm really confused about is the relationship between temperature and resistance. Some sources say one thing, others say the other.
- A rise in temp means that there are more free electrons which are free to move.
sooo => (this sort of links in with the previous question) when there's more free delocalised electrons, does this mean that resistance increases as they inhibit current flow?? Or have i got it completely wrong?!

Urgent responses needed, and +rep is available, thanks
2. (Original post by sweetascandy)
Okay, so here's what I do know:
- Current flows from +ive to -ive, the opposite direction to which electrons flow.
- Current and resistance are inversely proportional to each other. So as I increases, R decreases.
=>SO does that mean resistance kinda encourages electron flow to limit the current?

One other thing I'm really confused about is the relationship between temperature and resistance. Some sources say one thing, others say the other.
- A rise in temp means that there are more free electrons which are free to move.
sooo => (this sort of links in with the previous question) when there's more free delocalised electrons, does this mean that resistance increases as they inhibit current flow?? Or have i got it completely wrong?!

Urgent responses needed, and +rep is available, thanks
No. Resistance is inversely proportional to the cross-sectional area of a conductor, or its conductive properties - and the bigger the area of a conductor, and the more free electrons it has packed in, the more electrons (hence current) can move.

I don't get the second part; I'm not sure you have the concept of resistance quite clear.
3. For understanding current, it doesn't actually matter whether you treat it as flowing from 'positive to negative' on a battery. You're free to choose your maths as if it was going the other way round and it would work the same, but with the pluses and minuses flipped - positive to negative is just how people are used to doing it.

A current is a flow of a electrons. Resistance in a circuit is something which tries to stop this flow of electrons - for example, the electrons might collide with the rubber on the outside of the copper wire, and lose energy, therefore they don't flow as fast. So yes, you can think of it as resistance limiting the current.

About temperature: The problem comes because different substances change in different ways as you increase the temperature! Normally, increasing the temperature increases the resistance in the circuit. This is because of effects like the electrons colliding with the outside of the copper more often because they have more energy.

However, in special circumstances, raising the temperature will decrease the resistance because as you said, the temperature frees up more charge-carrying electrons. These materials in which this happens are called semiconductors. You might also hear of thermistors, which are a type of component often made out of semiconductors so that they lose resistance with heating.

Hope that helps
4. (Original post by Clip)
No. Resistance is inversely proportional to the cross-sectional area of a conductor, or its conductive properties - and the bigger the area of a conductor, and the more free electrons it has packed in, the more electrons (hence current) can move.

I don't get the second part; I'm not sure you have the concept of resistance quite clear.
You're talking about a completely different equation. I said that R is inversely proportional to I, because of the equation 'V= IR" or "R=V/I".
5. Yeah, you don't need to worry about cross-sectional area. V=IR implies that resistance limits current, as I said above
6. (Original post by Xdaamno)
For understanding current, it doesn't actually matter whether you treat it as flowing from 'positive to negative' on a battery. You're free to choose your maths as if it was going the other way round and it would work the same, but with the pluses and minuses flipped - positive to negative is just how people are used to doing it.

A current is a flow of a electrons. Resistance in a circuit is something which tries to stop this flow of electrons - for example, the electrons might collide with the rubber on the outside of the copper wire, and lose energy, therefore they don't flow as fast. So yes, you can think of it as resistance limiting the current.

About temperature: The problem comes because different substances change in different ways as you increase the temperature! Normally, increasing the temperature increases the resistance in the circuit. This is because of effects like the electrons colliding with the outside of the copper more often because they have more energy.

However, in special circumstances, raising the temperature will decrease the resistance because as you said, the temperature frees up more charge-carrying electrons. These materials in which this happens are called semiconductors. You might also hear of thermistors, which are a type of component often made out of semiconductors so that they lose resistance with heating.

Hope that helps
Thanks a lot, and yeah it does make a lot of things clear. So are the number of electrons inversely proportional to the current, or am I just thinking way too much into things?! +rep gone your way. :-)
7. It's fine, hope that's alright. Actually, as the number of free electrons goes up, the current also goes up - because it's easier for charge to flow if there's more charge there.

(Careful with using 'inversely proportional', too - that has a specific meaning, which is that as you double one value, the other value halves. That happens to be true for current and resistance but not for most things. That's neither here nor there though, once you get the ideas solid the other knowledge builds on that.)
8. (Original post by Xdaamno)
It's fine, hope that's alright. Actually, as the number of free electrons goes up, the current also goes up - because it's easier for charge to flow if there's more charge there.

(Careful with using 'inversely proportional', too - that has a specific meaning, which is that as you double one value, the other value halves. That happens to be true for current and resistance but not for most things. That's neither here nor there though, once you get the ideas solid the other knowledge builds on that.)
Okay one more thing: so for metals, high temp increases R. This is becoz as the electrons gain energy, they collide more with the metal ions. I understand this much. So does more collisions mean that it'll slow the current down?! I'm struggling to link the collisions part with resistance. thanks btw
9. Right, so, yeah, for non-semiconducting metals, which is what you're talking about, the resistance goes up with temperature. Let me try and explain it this way:

As the electrons are moving through the metal, with a higher energy, they're often hitting the ions and bouncing around the place. If they're generally moving in one direction - a 'current' - when they hit the ions, they'll often bounce backwards off them. Therefore, on the whole, this will cause the electrons to flow slower. It's just like putting rocks in a flowing river, but use your imagination to think that as the temperature goes up, the rocks are hit more often.

The tricky part you're struggling with seems to be linking this with the words 'current' and 'resistance', right? Current is basically a measure of how fast the electrons are flowing through the metal, and resistance is a measure of how much the metal is trying to stop them flowing. As you increase the temperature, the metal ions do a better job of stopping the electrons flowing, and so resistance can be said to increase - therefore it follows that, since I=V/R, the current will decrease.

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