Dielectric Sphere in Uniform Field

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SUMMARY

The discussion focuses on the boundary conditions for the electric potential, \Phi, outside a dielectric sphere in a uniform electric field. Specifically, it addresses the condition that \lim_{r→0}\Phi(r,θ) must remain finite. The reasoning provided involves the application of the Coulomb formula, which states that the potential \Phi at a point \mathbf{x} is derived from the charge density \rho within a finite volume V. As the distance from the charge increases, the potential approaches zero, confirming the necessity of the boundary condition.

PREREQUISITES
  • Understanding of electrostatics and electric potential
  • Familiarity with Coulomb's law and charge density concepts
  • Knowledge of boundary conditions in electrostatics
  • Basic calculus for evaluating integrals
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This discussion is beneficial for physicists, electrical engineers, and students studying electromagnetism, particularly those interested in the behavior of dielectric materials in electric fields.

Apteronotus
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Hi,

One of the boundary conditions when solving for the potential, \Phi, outside a dielectric sphere placed within a uniform electric field is
\lim_{r→0}\Phi(r,θ)<\infty

Can anyone explain/prove why this so.

Thanks,
 
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If the charges are contained in some finite volume ##V##, then the Coulomb formula applies:

$$
\Phi(\mathbf x) = \int_V \frac{\rho(\mathbf r)}{4\pi |\mathbf x-\mathbf r|}\,d^3\mathbf r.
$$

If total charge in the volume ##V## is finite, the integral can be estimated by (is lower than) ##Q/(4\pi |\mathbf x-\mathbf r|)## for some ##Q##. As the latter expression falls off to zero as distance increases, so does the potential.
 
Thank you Jano!
 

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