00:03
All right, looks like your questions are involving resistivity, resistance, and how it affects current flow, and a little bit about circuit diagrams at the end.
00:17
So i'll go through all of this here.
00:21
Question one is about how is resistivity affected by the length of the wire, the resistivity of the wire itself, and then the cross -section.
00:34
Area, so i put out the equation for resistance.
00:39
And i'll just label them and talk a little bit about each of these.
00:43
So this is the length of the wire, is this cursive l.
00:50
And that's usually measured in meters.
00:54
And then we also have the area, cross -sectional area, should say.
01:02
So that's another way of saying the thickness of it.
01:04
We oftentimes call it the gauge, if we're the gauge of the wire, if we're talking about being electricians.
01:14
That's usually measured in square meters.
01:19
And then we have the resistivity, which is this lowercase, looks like a p.
01:30
And this is unique for each material.
01:33
So each material has a different resistivity.
01:36
So copper has a high, a very low resistivity, i should say.
01:41
That allows it to have a low resistance.
01:44
Other materials that may be considered an insulator have very high resistivity.
01:50
So those would be, those would have high resistance in them.
01:54
So how do they all relate to the resistance? so resistance is the capital all over here.
02:00
So the length and resistivity are directly related to resistance.
02:05
So if i double the length, that is going to double the resistance.
02:09
So that's the trade -off with using wiring.
02:12
If it takes a lot of wire to wire the house, that's going to increase the overall resistance of the household circuit.
02:21
If i have a certain material that i'm using mainly copper is what we use in our house that has a low resistivity.
02:32
However, i changed aluminum wiring.
02:35
That's going to have a different resistivity.
02:37
It's going to increase the resistance.
02:39
Again.
02:42
And then the thickness of the wire is an inverse relationship.
02:46
So if i increase the thickness of the wire, the cross -sectional area, that's going to decrease the resistance, which makes sense.
02:54
It's like i'm widening the area that the electrons or the charge can flow through.
03:02
That's going to decrease the resistance.
03:04
Just the same as if i was using the water pipe, the wider that water pipe, is the more water that can flow through it in any given moment.
03:15
So it's very similar to that.
03:17
So the cross -exsectional area or thickness is going to lead to a lower resistance if i increase that.
03:26
So that's number one.
03:28
Number two is how does temperature affect resistivity? well, it depends on if we have an insulator or a conductor.
03:35
If i cool off an insulator, that decreases its resistivity.
03:58
So what that means is that as we cool off the insulator, it can actually become a better conductor.
04:05
So the colder the insulator becomes the more current flow can flow through it.
04:12
That's why we oftentimes, when we talk about superconductors, they're actually very cold, what we would normally see as an insulator.
04:22
If we cool those way down, we can get them to be very good current flow conductors instead.
04:30
So superconductors are almost always made out of super -cooled insulators if they're at room temperature.
04:39
So the opposite is happening with a conductor.
04:43
If i heat a conductor, i will cause an increase in resistivity.
05:00
Excuse me, a decrease in resistivity.
05:12
If i can spell.
05:25
So the opposite.
05:27
Conductors get better if we heat them up.
05:30
Insulators get better at conducting electricity if you cool them down.
05:34
So the opposite effects.
05:38
So now we get to the differences between parallel and series circuits.
05:43
So a parallel circuit i've drawn right here on the left and then a series on the right.
05:48
And there's mainly, they basically act in an opposite fashion.
05:53
So we'll talk about the voltage, the current flow, and the total resistance.
06:02
So on a parallel circuit, as resistors are added, resistance, actually decreases, which is the opposite of what happens on a series circuit.
06:34
So adding resistors on a series circuit causes an increase in resistance.
06:56
So if we had, say, for example, 10 -on resistors on here on our parallel circuit, and then we add them on our series circuit.
07:08
The total resistance on this parallel circuit here, assuming that the 9 -volt battery has no internal resistance, the total resistance on this circuit is 5, actually less than either of those two resistors.
07:26
Over here, the resistance total is now 20.
07:30
So we're adding them over on this side...