# magnetism (B)

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#1
Hello, can anyone help me with this, I'm starting a new course in a couple of weeks and I'm trying to read up on material but this is confusing me.

B = magnetic flux density
H = magnetic field strength

But I've also seen B being described as;

1 - The magnetic field [B]

2 - And also, that the magnetic field strength is calculated by B =uI/2 pi r

But why is the magnetic field strength calculated in B, when H is the magnetic field strength?

On the videos I'm watching, no one ever speaks about Magnetic Flux, only magnetic field strength, but they always write it as [B]

Thanks for any help.
1
1 year ago
#2
magnets are confusing... Fortunately I didn't have to worry about H fields till I got to uni. ( we called H the magnetising field) but the nomenclature is pretty variable and adds an additional layer to the confusion if you're referring to different sources.

B field is the more easily understood and corresponds to the the magnetic field lines you can sketch with iron filings - I'd guess you might only have to worry about B fields atm (unless H field is in the spec) or just try to concentrate on B until you have to think about H.

if you want to learn this stuff for your own enjoyment probably get one first year undergraduate book on electricity and magnetism and at least the naming conventions should be consistent all the way through.
0
1 year ago
#3
(Original post by CJones02)
Hello, can anyone help me with this, I'm starting a new course in a couple of weeks and I'm trying to read up on material but this is confusing me.

B = magnetic flux density
H = magnetic field strength

But I've also seen B being described as;

1 - The magnetic field [B]

2 - And also, that the magnetic field strength is calculated by B =uI/2 pi r

But why is the magnetic field strength calculated in B, when H is the magnetic field strength?

On the videos I'm watching, no one ever speaks about Magnetic Flux, only magnetic field strength, but they always write it as [B]

Thanks for any help.
I can understand your confusion. Should magnetic field strength be B or H? It is not easy to answer.

In physics, there are many important similarities between electric and magnetic interactions. In electric interactions, the electric force is the product of electric field strength and electric charge. From the electric force equation, we can define electric field strength E at a point as force per unit charge exerted on a stationary positive charge.
-----Eqn(1)

In magnetic interactions, the magnetic force FB exerting on a moving charge q perpendicular to the magnetic field is
FB = qvB -----Eqn(2)

This equation “can” be used as the definition of the magnetic field to indicate both its magnitude and its direction.
-----Eqn(3)

However, the direction of magnetic force FB does not give us the direction of magnetic field B.

If we compare eqn(1) and eqn (3), we can see the similar “structure” of defining a field.

In University Physics, the magnetic field strength is usually denoted as B instead of H whereas in an engineering course, magnetic field strength/intensity is usually H and magnetic flux density as B.

In some older good electricity and magnetism books (Electricity and Magnetism by Oleg D. Jefimenko and Classical electrodynamics by John David Jackson), B is the magnetic flux density but there are also old electricity and magnetism books (The Feynman Lectures on Physics vol II, Sommerfeld’s electrodynamics book, Electricity and magnetism by Edward M. Purcell) which denote B to be magnetic field vector or strength.

If you think is just a notation issue, I would encourage you to look into a paper written by John J. Roche at Linacre College in 1999 titled “B and H, the intensity vectors of magnetism: A new approach to resolving a century-old controversy”. He concluded his paper with the following statement:
However, there appear to have been far too many competing interpretations and conflicting conventions for a consensus to emerge.
There was an earlier thread in TSR which discuss the difference between H and B which you may be interested.
https://www.thestudentroom.co.uk/sho...php?p=64387847

https://www.thestudentroom.co.uk/sho...5&postcount=15
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