Not having a good understanding of Gauss's Law

[member 392791]

Hello,

So I had been studying Gauss's Law yesterday, and I still don't feel like I have an excellent grasp of it. I wonder, why is it when there is cylindrical symmetry, sometimes it seems you need to calculate the E coming from both ends of the gaussian surface, but other times only out of one. How do I know when to use which?


Also, my mind is still blown how you can just take a little chunk of an infinite surface and still calculate its electric field, it feels like I'm still not convinced, even though I know it must be true, I haven't wrapped my head around it. Can anyone maybe attempt to help me understand?

 

[DrZoidberg]

..., sometimes it seems you need to calculate the E coming from both ends of the gaussian surface, but other times only out of one. How do I know when to use which?

If you have two parallel plates i.e. a capacitor, nearly the entire field is in between the plates and outside the field is practically 0. That means when you calculate the flux of one of the plates it leaves the plate in only one direction. However if there is only one plate the field is equally strong on both sides and so the flux "splits". Half the flux leaves the plate on one side and the other half leaves it on the other side.