# B Some formulas (electromagnetism)

1. Jul 9, 2017

### DesertFox

dH=dl/dt
dB=dl/dx
dE/dB=-dx/dt
dD=dl/dx
dH/dD=-dx/dt

H - magnetic field strength;
B - magnetic flux density;
D - electric displacement field.

Please, have a look at these equations. Are they correct?
I can't grasp the idea. Any explanations?
I need some intuitive understanding of this formulas (if they are correct) and some knowledge about how they are derived...

I will be grateful for every comment...

Wish you everybody a nice day!!

2. Jul 10, 2017

### Ibix

Three of these formulas have infinitesimals on one side only. Coupled with your other two threads, they mean you need a better textbook.

3. Jul 10, 2017

### DesertFox

"Three of these formulas have infinitesimals on one side only."
All of these formulas have infinitesimals on both of the sides... d - for infinitesimals.
Could you be more specific about "the three formulas with infinitesimals on one side only"?
Thank you!

4. Jul 10, 2017

### Ibix

dH is infinitesimal. dl/dt is not infinitesimal.

As I asked you on your breaking strain thread, please provide a reference. This is either nonsense or there is a lot of context I'm missing.

5. Jul 10, 2017

### DesertFox

I am translating the text. But that is all the context! He is expressing relationship between, for example, H (magnetic field strength) and dl/dt (which is related to "wave").... and that is all, believe me! His book is compilation of short fragments (numbered 1, 2, 3....) and he is really brief... that's why everything is so mysterious and puzzling. So, please, if you have any ideas what can be- help me. People in this forum have much more knowledge in Physics than me- i am not arguing.....

6. Jul 10, 2017

### DesertFox

There is no more context!
The only clue: dl, dt and dx have something to do with WAVE.

7. Jul 10, 2017

### Ibix

As I pointed out in the other thread, PF rules require you to provide a reference when asked. Please do so.

8. Jul 10, 2017

### DesertFox

Jordan Metodiev, Bulgarian author (engineer, philosopher, writer), "Philosophical Tractate on Physics" (2014),
I can give link to the original text, but it is not in English.

I hope this information (proper reference) will be useful for finding answer to my questions.
The full context is translated by me and it contains in my questions (in my threads).
Thank you!

9. Jul 10, 2017

### Ibix

10. Jul 10, 2017

### DesertFox

But my suggestions is: let's discuss concepts, ideas formulas.... not the author, not the proper reference, not the PF rules.... but concepts, ideas, formulas.

I do my best to ask my question clearly, providing all the context which I have. If something in my post is not clear- I can try to make it even more clear.
That's not the issue.
Here it is, for example, the whole fifth fragment! This is the original text without translation:

5.

dH =dl/dt; dB = μodH = dl/dx; dE/dB = - dx/dt; dE = dl/dt; dD = εodE = dl/dx; dH/dD = - dx/dt.

Физичната вълна се "улавя" в т. нар. магнитоелектрично поле

Фарадей: dE/dB = - dx/dt; B/H = μo (дефинитивно);

Максуеловата добавка към Ампер: dH/dD = - dx/dt; D/E = εo (дефинитивно);

E, H - вектор на електричната и вектор на магнитната напрегнатост;

D, B - вектор на електричната и вектор на магнитната плътност;

x ┴ t ┴ dx/dt - пространствената координата, времевата координата и

скоростта на разпространение (времепространствената причинност); т. е. тук става

въпрос за онагледяване (символична стереометрия) на вълновата аналитика (скорост

на разпространение в пространство-времето), като едното от пространствените

измерения е отделено въобще за пространството... Бездарието подменя

действителността с... фактология. Математическият език (спрямо музикалния) има

това незаменимо аналитическо предимство, щото да разделя компонентите на

достатъчното основание, а именно: времето, пространството и причинността и да

координира анализа; и невям в "синтетическа употреба" (палиативът на

творчеството) се изразява "порокът" на математическия изказ: фабрикува се во

истине факто-логия, за която възвратно да се твърди, че е "математически

моделирана". И ето как битието се сдобива "свише" със субстанциалност, т. е. твърд,

сиреч устой; за да могат бездарниците, щъкайки, да не си знаят мястото... Това,

което на философа липсва у едно строго фактологическо изложение, е тълкуванието

(нямам предвид бабините деветини); предозираните факти убиват боговете и раждат

философите... И ето че теорията на относителността иде не само да детронира т. нар.

абсолют, но и да предложи живеца... εo, μo - електричната и магнитната вакуумна

проницаемост.

(A) dE/dx = - dB/dt;

d/dx(dE/dx) = - d/dx(dB/dt);

d2E/dx2 = - d/dt(dB/dx) = - μod/dt(dH/dx);

d2E/dx2 = εoμod2E/dt2. (dH/dx = - dD/dt; dD = εodE.)

(B) dH/dx = - dD/dt;

d/dx(dH/dx) = - d/dx(dD/dt);

d2H/dx2 = - d/dt(dD/dx) = - εod/dt(dE/dx);

d2B/dx2 = εoμod2B/dt2. (dH = dB/μo; dE/dx = - dB/dt.)

(A + B) d²(E+B)/dx² = [√(εoμo)]²[d²(E+B)/dt²].

11. Jul 10, 2017

### Ibix

Get a better textbook.

He's got the infinitesimal equal to something finite problem I already pointed out.

If you combine his first and fourth equations (which are wrong, see above) then he says E=H.

The Faraday-Maxwell equation says that $$\nabla\times \vec E=-\frac {\partial \vec B}{\partial t}$$In the specific case of an electric field pointing perpendicular to the x direction this reduces to $dE/dx=-\partial B/\partial t$. He says that this special case is a definition, which seems to lack context at best. He also simply ignores the "partial" bit of the partial differential with no justification. Then he writes $dE/dB=-dx/dt$. Um.

And finally his last equation adds together two quantities (E and B) which have different units. No.

Get another text book. Any other textbook.

Last edited: Jul 10, 2017
12. Jul 10, 2017

Staff Emeritus
Fair enough. What you've posted is gibberish. (Infinitesmal on one side)

13. Jul 10, 2017

### Ibix

Just to add: the reason academics - not just PF - require references is so that we can sort out what you say from what the original author said. It's a matter of intellectual honesty to do your best to be clear about where information comes from, and whose work you are relying on. It makes it easier to stop mistakes spreading and to localise them when they do.

In this case it is helpful to have seen the original text because I'm now convinced it's a poor one. It's not you having difficulty understanding; it's the text you're trying to understand. Learn from another source.

14. Jul 10, 2017

### Staff: Mentor

This is not a good source. You should immediately stop trying to understand it and instead spend your time trying to understand a standard high quality textbook. We cannot help you other than to point out that the source is bad.

15. Jul 10, 2017

### DesertFox

Let's have a look at the first equation: dH=dl/dt
We have inifinitesimal on the left side, OK. But dl/dt can be regarded (and treated as!) as inifinitesimal, too. I can't understand what is the problem with that.
Excuse me for my tenacity.. I can't understand your specific critique.......

16. Jul 10, 2017

### weirdoguy

How?

17. Jul 10, 2017

### DesertFox

How? Call it a priori. Call it imagination.
Mathematics are not postulate from God, they are instrument (device) of our human thinking.

18. Jul 10, 2017

### weirdoguy

Yes, and those instruments don't work the way you claim they do. Please provide reference for what you said.

19. Jul 10, 2017

### DesertFox

How can i provide you reference for the fact that 1+1=2 ?
infinitesimal / infinitesimal gives you infinitesimal, it is simple like this.

20. Jul 10, 2017

### weirdoguy

It's simply not true. You don't understand how infinitesimals work.