Possible Error in Vector Calculus Book

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Discussion Overview

The discussion revolves around potential errors in the presentation of Maxwell's equations in a vector calculus textbook, specifically addressing the definitions and representations of electric and magnetic fields. Participants explore the implications of these definitions and their consistency with established physics concepts.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant identifies what they believe to be errors in the representation of Maxwell's equations, particularly regarding the definitions of the electric field (E) and magnetic field (H).
  • Another participant suggests that the book may be using Heaviside units, which do not include constants like epsilon zero and mu zero, and emphasizes the importance of using the correct notation for divergence.
  • There is a discussion about the varying definitions of H and B across different texts, with some participants noting that terminology can differ significantly.
  • A participant clarifies that the term "magnetization" refers to the magnetic moment per unit volume and discusses the relationship between B and H fields.
  • One participant mentions the practical aspects of using H and E fields in laboratory settings, highlighting the direct control of H through currents.

Areas of Agreement / Disagreement

Participants express differing views on the definitions and representations of the fields in Maxwell's equations, indicating that multiple competing interpretations exist. There is no consensus on whether the textbook contains errors, as some participants defend the terminology used.

Contextual Notes

Participants note that the definitions of H and B can vary widely among different sources, which may contribute to the perceived discrepancies. The discussion does not resolve the potential errors or clarify the correct terminology definitively.

Dahaka14
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There is a section that contains dealings with Maxwell's equations in my vector calc book, and there are, to my belief, numerous errors. Some of them I am certain on, but the is one I am not so sure on, although it would be a bigger blunder.

The book describes Maxwell's equations as, having E as electric field and H magnetic field:
[tex]\nabla[/tex][tex]\cdot[/tex]E=[tex]\rho[/tex]
[tex]\nabla[/tex][tex]\cdot[/tex]H=0
[tex]\nabla[/tex][tex]\times[/tex]E+[tex]\partial[/tex]B/[tex]\partial[/tex]t=0
[tex]\nabla[/tex][tex]\times[/tex]H-[tex]\partial[/tex]D/[tex]\partial[/tex]t=J

Aside from current density J not being bold due to being a vector, from what I know if one wishes to write maxwell's equations without using constants, they must be written:
[tex]\nabla[/tex][tex]\cdot[/tex]D=[tex]\rho[/tex]
[tex]\nabla[/tex][tex]\cdot[/tex]B=0
[tex]\nabla[/tex][tex]\times[/tex]E+[tex]\partial[/tex]B/[tex]\partial[/tex]t=0
[tex]\nabla[/tex][tex]\times[/tex]H-[tex]\partial[/tex]D/[tex]\partial[/tex]t=J

Second, they defined H as magnetic field, when it is magnetization. Is there something wrong here?
 
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It would help if you named the book and author thereof.
The book is probably using "Heaviside units", which are rationalized without the
epsilonzero and muzero. You should use \cdot to get the divergence right.
You are right about the D and B in the first two equations.
The names given to B and H vary widely among different books.
Some books call H "magnetic field", others call B "magnetic field".
I prefer the term for B, which is the physical magnetic equivalent of E.
The names used for B are even more varied and confusing.
"Magnetization" is always used for the magnetic moment per unit volume
(to within varying factors of 4 pi). In your units, it would equal M=B-H.
Your book probably just wants to demonstrate the math, and doesn't care much about the physics.
 
Sorry about the LaTex, it's the first time I've ever used it. I had the /cdot in before, but I must've deleted it while trying to make it look better.
The book is Vector Calculus (5th Edition) by Jerrold E. Marsden and Anthony J. Tromba.
Actually, I just noticed, the dot is there at the upper right corner of the del, but I DID have it look like a divergence before as aforementioned.
 
Last edited:
In a lab setting, physicists deals with the H field and the E field. This is because we use currents to create a magnetic field, and H is what we control directly. That is, B is dependent on H, but we can always directly control H. However, we use potentials to create an electric field directly.
 

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