Electric Fields in Coaxial Cables: Understanding Bound Charge Densities

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SUMMARY

The discussion centers on the behavior of charge densities in coaxial cables, specifically addressing the assumption that the linear charge density (λ) on the inner conductor is equal to the negative of the linear charge density (-λ) on the outer shell. It is established that while bound charge densities due to polarization are present in dielectrics, they do not contribute to the total charge, which is why the charge densities remain equal. The presence of a dielectric with a relative permittivity (ε_r) greater than 1 increases the capacitance (C) compared to a coaxial cable without a dielectric.

PREREQUISITES
  • Understanding of electrostatics and charge distributions
  • Familiarity with coaxial cable structures
  • Knowledge of dielectric materials and their properties
  • Basic grasp of capacitance calculations in electrical engineering
NEXT STEPS
  • Study the effects of dielectric materials on capacitance in coaxial cables
  • Learn about bound charge densities and their role in polarization
  • Explore the mathematical derivation of capacitance in coaxial cables with dielectrics
  • Investigate the implications of varying ε_r on electric field distribution
USEFUL FOR

Electrical engineers, physics students, and anyone studying the principles of electrostatics and coaxial cable design will benefit from this discussion.

PhysicsPrincess
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Homework Statement


http://postimg.org/image/vzhqi8er5/
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Homework Equations

The Attempt at a Solution


I understand all the calculations here - http://www.physicspages.com/2012/10/18/coaxial-cable-with-dielectric/
I have one issue that is bugging me though - if λ charge density is distributed over the inner conductor, why can it be assumed that the same -λ is distributed over the outer shell? Aren't there any bound charge densities involved here?

Thank you.
 
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With bound charge densities you mean the polarization ? That is involved. That's why (for ##\epsilon_r > 1##) C is greater than for the same coax without the dielectric. But the ##\lambda## are the same: polarization has no total charge.
 
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