# A The magnetic field within cylindrical hollow conductor

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1. Oct 24, 2016

### nabil25

Hi,
While studying the coaxial cable, i noticed that the magnetic field of the inner conductor can pass through the hollow conductor (can be calculated in the region 3). However, the boundary condition of the magnetic field at the surface (between dielectric and perfect conductor) of a perfect conductor is known as the tangential component of H (Ht = Js surface current density) and the normal component is Hn = 0. Inside the perfect conductor, we have Ht = 0 and Hn = 0.

So why do we superpose the magnetic field of the inner conductor and the hollow conductor when calculating the magnetic field in the region 3 ?

In this case we suppose that the current flowing in the inner conductor is i1 and in the hollow conductor is i2 (not like the coax,here i2 is not equal to -i1).

Thank you in advance.

2. Oct 25, 2016

### kuruman

What makes you say this?

3. Oct 25, 2016

### nabil25

According to the literature, it's the boundary condition of the magnetic field at the interface of dielectric-perfect conductor.

4. Oct 25, 2016

### kuruman

The literature does not say that the H-field is zero inside the conductor. What does the literature say?

5. Oct 25, 2016

### nabil25

The litterature say that the magnetic field inside a perfect conductor is equal to zero. If it's not a perfect conductor, the magnetic field will penetrate until the skin depth.

6. Oct 25, 2016

### nabil25

"The second type of interface discussed here is that between a perfect dielectric and a perfect conductor. In this case, the
overriding condition is that of the conductor, that is, that all fields in the perfect conductor must be zero. Assuming material
(2) is the perfect conductor, E2t, H2t, D2n, and B2n are zero"

7. Oct 25, 2016

### DarkBabylon

Can you reference where that comes from? One would expect it would be explained somehow there.

8. Oct 25, 2016

### nabil25

ebook (Engineering electromagnetics) Nathan Ida. third edition. page 581. there is a lot of references that say the same thing.

9. Oct 27, 2016

### vanhees71

Well, at this page are only the usual boundary conditions for the electromagnetic field components but no such claim. Perhaps you are referring to the Meissner-Ochsenfeld effect in superconductivity? Then have a look at Wikipedia

https://en.wikipedia.org/wiki/Meissner_effect

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