Conceptual question on field/displacement

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SUMMARY

The discussion centers on the relationship between electric field (E) and electric displacement (D) in dielectrics, specifically addressing the confusion regarding the directionality of polarization and its effect on macroscopic fields. The equation D = εE is established, where ε represents permittivity, and the inverse relationship E = κD is also defined. The participant concludes that the key to understanding this relationship lies in recognizing the superposition of fields from multiple dipoles, which results in a net field that aligns with the polarization direction.

PREREQUISITES
  • Understanding of electric fields and dielectrics
  • Familiarity with the concept of polarization in materials
  • Knowledge of Maxwell's equations
  • Basic principles of superposition in physics
NEXT STEPS
  • Study the concept of electric displacement in detail, focusing on its role in dielectric materials
  • Explore the derivation and implications of the equations D = εE and E = κD
  • Investigate the principles of polarization and how it relates to macroscopic electric fields
  • Examine the superposition principle in the context of electric fields generated by dipoles
USEFUL FOR

Students of electromagnetism, physicists, and engineers working with dielectric materials and electric field applications will benefit from this discussion.

johng23
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I have a very basic problem in understanding the relationship between electric field and displacement. If a field is applied to a dielectric, it is clear that this will cause the material to polarize, and one can define the permittivity of the material to quantify the size of this effect. Since we can write [itex]D=\epsilon E[/itex], we can also define the inverse permittivity [itex]E=\kappa D[/itex]. But conceptually, I can't make sense of the displacement as the independent variable. How does a polarization give rise to a macroscopic field in the same direction? If anything, a polarization seems associated with a field in the opposite direction (by imagining the situation in the center of a dipole), although I know that macroscopic E&M says nothing about these microscopic fields.

If I think about the case of stress and strain, I can easily imagine how either one gives rise to the other. Where is my problem?
 
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Ok, the answer is just to take the superposition of the fields from many dipoles. Everything should cancel except the field parallel to the polarization.
 

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