Dielectric Sphere with Free Volume Charge

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SUMMARY

The discussion focuses on calculating the electric displacement field D(r) within a dielectric sphere containing a free volume charge. Using Gauss' Law, the user attempts to derive D(r) for the region where r ≤ a, leading to the equation D = P₀r² / (3a). The confusion arises from the assumption of a constant charge density ρ, which is incorrect in this context. The correct approach requires acknowledging the variable nature of ρ within the dielectric material.

PREREQUISITES
  • Understanding of Gauss' Law in electrostatics
  • Familiarity with dielectric materials and their properties
  • Knowledge of electric displacement field concepts
  • Basic calculus for integrating over volume and surface
NEXT STEPS
  • Review the derivation of electric displacement fields in dielectric materials
  • Study the implications of variable charge density in electrostatics
  • Learn about the relationship between electric field E, displacement field D, and polarization P
  • Explore advanced applications of Gauss' Law in non-uniform charge distributions
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Students and professionals in physics and electrical engineering, particularly those studying electrostatics and dielectric materials.

jegues
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Homework Statement



See figure attached.

Homework Equations





The Attempt at a Solution



I'm confused as to how they got their D(r)

Using Gauss' Law,

For r < or = a

[tex]\oint_{S} \vec{D} \cdot \hat{n} dS = \int_{v} \rho dv[/tex]

[tex]D(4 \pi r^{2}) = \frac{\rho 4 \pi r^{3}}{3}[/tex]

[tex]\Rightarrow D = \frac{P_{0}r^{2}}{3a}[/tex]

What am I doing wrong?
 

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You have ρ = constant. It's not.
 

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