Dielectric constant refractive index relationship

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Discussion Overview

The discussion revolves around the relationship between the dielectric constant and the refractive index, specifically in the context of water. Participants explore the apparent discrepancy between the values of the dielectric constant and the refractive index, questioning how they relate to each other and the implications of frequency dependence.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that the refractive index of water is 1.333 while the dielectric constant is 80.1, expressing confusion over the apparent inconsistency with the relationship that the refractive index equals the square root of the dielectric constant.
  • Another participant suggests looking at the definitions of the dielectric constant and refractive index, indicating that their relationship involves the speed of light.
  • It is pointed out that both the dielectric constant and the index of refraction are frequency-dependent, and that the values should be measured at the same frequency for a valid comparison.
  • A participant clarifies that the dielectric constant value of about 80 is relevant at DC or very low frequencies, while the refractive index of 1.33 pertains to visible light frequencies.

Areas of Agreement / Disagreement

Participants generally agree that frequency dependence plays a crucial role in the relationship between dielectric constant and refractive index. However, there is no consensus on the implications of this relationship or how to reconcile the specific values presented.

Contextual Notes

The discussion highlights the importance of frequency in determining the values of dielectric constant and refractive index, indicating that the measurements are not directly comparable without considering this factor.

tomas632
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hi, i have seen on another topic here that the refractive index equals the square root of the dielectric constant. from datasheet values we have...

water refractive index = 1.333
dielectric constant = 80.1

Without even doing the calculation its obvious that the square root of 80.1 is not 1.333...im clearly missing something here, can somebody help me with this please?

Thanks

Tom
 
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Both dielectric constant and index of refraction depend on frequency.
When you write the relationship between them the values should be measured at the same frequency.
The value of about 80 is water's dielectric constant in DC regime or at very low frequency.
The 1.33 is the index of refraction at the frequency of visible light (about 10^14 Hz).
 
in general the refractive index is equal to the sqrt(dielectric constant), but you have to notice the frequency dependence as mentioned by nasu (the previous Post)
 

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