00:01
Okay, we have three concentric spherical gaussian surfaces.
00:05
We have surface a, surface b, and surface c, and those are spheres.
00:20
So a, b, c.
00:23
Inside surface a is a positive point charge, q, and inside surface c, but outside b and a, is a charge minus q.
00:36
So what is correct about the magnitude of the electric flux through the three surfaces? okay, so gauss's law tells us that the electric flux for a spherically symmetric surface is the charge enclosed divided by the constant epsilon knot.
01:00
The other way to think about this, if you don't want to think about it mathematically, is flux is just the amount of something that is entering a surface or exiting a surface.
01:14
So we have these field lines coming off of the charges, right? and we'll do it in blue, i guess.
01:20
So from this q charge, we have all these field lines that are going out.
01:26
And we'll just think of the q and the minus q is separate.
01:30
We won't think of what the electric field actually looks like.
01:33
So we've got all these field lines coming out, right? so these are all exiting the surfaces.
01:44
And it's not entering any of the surfaces, so it's all going to be positive flux, right? if you're exiting a surface, that's usually defined as a positive flux.
01:55
So all of the surfaces are going to get a positive flux from that charge, or plus q.
02:03
And then if we think about the minus q charge, it's going to do the same thing.
02:08
So we can kind of imagine all these field lines passing through, and i'm kind of skewing this so that they pass through every single.
02:21
So i'm showing them pass through all the surfaces.
02:23
Okay, look at surface a.
02:26
You see the field lines go in, and then they come out.
02:29
They go in, they come out, in and out.
02:32
So surface a is actually getting no net flux because of the minus q charge...