🧵 Physics playing fast and loose with math again?
Anonymous at Tue, 7 May 2024 17:29:53 UTC No. 16164224
So we've obtained an expression for E for a charged particle on the axis of symmetry of a charged circle that's producing the field.
Now they go "hey but let's make this totally finite E and q differentials and then go from there" - WTF?
Does that have something to do with the fact that going from a point to a circle (0-D to 1-D) is like integrating a differential and going from a circle to a disk (1-D to 2-D) is analogous so a finite quantity (q and E) in 1-D becomes infinitesimal in 2-D? Is that what it is?
Anonymous at Tue, 7 May 2024 17:56:40 UTC No. 16164264
>>16164224
or is it just one of those "don't pay too much attention to it lol it gives the right results xDDD"
Anonymous at Tue, 7 May 2024 18:09:45 UTC No. 16164284
>>16164224
I dont see anything wrong with the math here. This is a typical exercise.
Anonymous at Tue, 7 May 2024 19:28:06 UTC No. 16164465
Basically yes. Infinitesimal thin ring is not measurable in 2D. But it has proper lenght in 1D i.e. 2 pi r
Anonymous at Tue, 7 May 2024 20:15:12 UTC No. 16164548
>>16164284
What's the difference between a cylinder and a disk?
Anonymous at Tue, 7 May 2024 20:44:19 UTC No. 16164614
>>16164548
One is humble enough to stay in 2D, another decided to betray it's roots to try luck in 3D cause muh volume
Anonymous at Tue, 7 May 2024 20:49:18 UTC No. 16164626
>>16164224
Ok I REALLY don't get this one
I assumed H2O is a dipole because on one side you have O that has 2 electrons closer to it than two H's so on average there's a dipole along the line of symmetry which q is 2e.
But here they just use all of protons and all of electrons despite the fact that on one side there are 2 protons and parts of 2 electrons and on the other it's 8 protons and bigger parts of those 2 electrons. But where do they get 10e (that's supposed to be on both sides with different signs) from???
Anonymous at Tue, 7 May 2024 21:15:19 UTC No. 16164672
>>16164224
I feel like a lifetime ago, I have seen this exact diagram. Is it in a generic book like "University Physics"?
Anonymous at Tue, 7 May 2024 21:56:22 UTC No. 16164757
>>16164672
It's Fundamentals of Physics. But obviously it's a common drawing since a problem like this is discussed in any serious textbook on CED
Anonymous at Wed, 8 May 2024 07:02:52 UTC No. 16165399
>>16164224
does anybody even care? this is a nothing burgerwith no real world application
Anonymous at Wed, 8 May 2024 08:53:42 UTC No. 16165520
>>16165399
> calculating interaction between charged bodies has no real world application
Touch silk
Anonymous at Wed, 8 May 2024 10:42:55 UTC No. 16165582
>>16164224
filtered by griffiths level physics. you are ngmi
Anonymous at Wed, 8 May 2024 11:21:54 UTC No. 16165630
>>16164548
Its a purely mathematical device.
An infinitely thin disk charged with some charge per unit area
Doing the exercise of a thick disk isnt any harder, you just have to do one more integration..
Anonymous at Wed, 8 May 2024 14:50:06 UTC No. 16165929
>>16164224
Shut up and calculate.
Anonymous at Wed, 8 May 2024 17:16:19 UTC No. 16166071
>>16164626
>I assumed H2O is a dipole because on one side you have O that has 2 electrons closer to it than two H's
Thats an incorrect assumption. Dipole happens because Oxygen have non-bonding valence electrons, which will generative repulsive forces against themselves and the ligands (hydrogen), resulting in the angled geometry. The lack of inversion centre in this geometry means that this molecule is polar, so there is a electronegative region (HIGHER ELECTRONIC DENSITY) and an electropositive region (LOWER ELECTRON DENSITY)
>But here they just use all of protons and all of electrons despite the fact that on one side there are 2 protons and parts of 2 electrons and on the other it's 8 protons and bigger parts of those 2 electrons
I am not sure how physicists deal with it (chemistfag here) but remember that the hydrogen will NEVER lose its single hydrogen. Oxygen isnt strong enough to poach it, and the whole deal of covalent bonding is to overlap orbitals and create new orbitals with lower energy requirements. In other words, Hydrogen will end with 2 electrons, not a minor part of 1. The magnitude is 10e because the molecule has 10 electrons, and afaik magnitude is a scalar quantity
Anonymous at Wed, 8 May 2024 17:49:53 UTC No. 16166119
>>16165630
I'm sorry.
I was being retarded.
Of course an infinitely long cylinder would have the exact same behavior as a 1 atom thick disk.
Apologies for my retardation.
Because it is dependent on r, R, and dr, and not h.
Anonymous at Wed, 8 May 2024 19:00:01 UTC No. 16166188
>>16166071
>The magnitude is 10e because the molecule has 10 electrons, and afaik magnitude is a scalar quantity
But there are only 8 protons on one side and two from both Hydrogens on the other side. And the electrons like you said are spread in a way that densities in two regions are different but how do we get this exact number of 10?
Anonymous at Wed, 8 May 2024 19:07:38 UTC No. 16166198
>>16164757
>>16164224
If it is just in a textbook, who cares? Read nigga, read. If it were in an instruction manual on how to build something or how to fly a plane, that's one thing. But this is supposed to teach you one concept and the best way to do that is to avoid any other concept not being taught.
Anonymous at Wed, 8 May 2024 20:13:44 UTC No. 16166278
>>16166188
You gotta hit the books for a more detailed information, I just know some chemistry
Anonymous at Thu, 9 May 2024 15:21:57 UTC No. 16167454
>>16164626
Look at what the question is asking for; it's asking for the distance between the center of all the electrons and the center of all the protons.
Anonymous at Thu, 9 May 2024 16:16:18 UTC No. 16167540
>>16167454
Oh so it's just an analog of a center of mass which given two types of charge gives you a dipole. Cool