What causes the magnetic field inside a coaxial cable?

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SUMMARY

The magnetic field inside a coaxial cable, specifically within the region defined by 0 > r > r1, is zero due to the nature of current distribution in the inner conductor. When the inner conductor is a cylindrical shell, the current does not enclose any magnetic field within that region. Conversely, if the inner conductor were a solid cylinder, the magnetic field would increase linearly with the radial distance from the center. This distinction is crucial for understanding electromagnetic behavior in coaxial configurations.

PREREQUISITES
  • Understanding of Ampère's Law
  • Familiarity with cylindrical coordinate systems
  • Knowledge of magnetic field concepts in electromagnetism
  • Basic principles of current flow in conductors
NEXT STEPS
  • Study Ampère's Law and its applications in cylindrical geometries
  • Explore the concept of magnetic fields in different conductor shapes
  • Learn about the electromagnetic theory related to coaxial cables
  • Investigate the effects of current distribution on magnetic fields
USEFUL FOR

Electrical engineers, physics students, and professionals working with electromagnetic theory and coaxial cable design will benefit from this discussion.

Prinsen
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Hi. In this task we're asked to calculate the magnetic field inside the small cylinder (0>r>r1). The answer is zero, which I don't quite understand...Here is the picture:
http://bildr.no/image/WTJ1VG5F.jpeg

As the picture shows there's a current I going through the inner cylinder. Wouldn't this current generate a magnetic field at a distance 0 >r>r1?
 
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From the shading it looks like the inner conductor is a cylindrical shell rather than a solid, in which case there will be no inside magnetic field.

If it's a solid conductor the magnetic field will increase linearly with r.
 
Ok, thanks. So the current "flows" along the cylindrical shell? I.e inside the shell we don't enclose any current.
 

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