Dielectric constant and index of refraction

In summary, the conversation discusses the difference between the dielectric constant and the index of refraction for water. The dielectric constant for water is 80, but the index of refraction is 1.33, likely due to different frequencies being used. This is because the index of refraction is dependent on frequency, while the dielectric constant is not. It is important to use the correct frequency when using these values for calculations, and the dielectric constant also varies with temperature.
  • #1
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I'm a little confused. My source says the dielectric constant for water is 80. Then I have the equation that gives the index of refraction as [itex]n=\sqrt{\epsilon_r}[/itex] (since it isn't very magnetic). But the index of refraction for water is 1.33. What am I missing?
 
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  • #2
They are both frequency dependent terms. However:

[tex] n(\omega) \equiv \sqrt{\epsilon(\omega)}[/tex]

So your value are obviously not for the same frequency, you need to figure out which one is correct for the given frequency - I would guess refractive index implies the frequency is for visible light.

And your dielectric constant = 80 is relevant for a completeley different frequency ie not visible light.
 
  • #3
Most quoted values for dielectric constant are for frequencies in the kHz, whereas visible light is hundreds of THz, so don't be surprised if there is a disrepancy. Refractive index values are measured at a standard optical frequency (Sodium D line perhaps, I'm not too sure).

What value you use obviously depends on what you are trying to solve.

Claude.
 
  • #4
Also varies with temperature.
DC = 80 corresponds to 80*F.(using radio frequency, Mhz). At 212*F, dielectric constant is ~53 for water.
:wink:
 

Related to Dielectric constant and index of refraction

1. What is the difference between dielectric constant and index of refraction?

The dielectric constant, also known as the relative permittivity, is a measure of how easily a material can be polarized in the presence of an electric field. It is a dimensionless quantity that is always greater than or equal to 1. On the other hand, the index of refraction is a measure of how much a material can bend light as it passes through it. It is also a dimensionless quantity, but is always greater than or equal to 1.

2. How are dielectric constant and index of refraction related?

The dielectric constant and index of refraction are related through the speed of light in a vacuum (c) and the speed of light in the material (v). The index of refraction is equal to the square root of the dielectric constant, which means that materials with a higher dielectric constant will have a higher index of refraction and vice versa.

3. How do dielectric constant and index of refraction affect the propagation of light?

The dielectric constant and index of refraction play a crucial role in determining how light propagates through a material. As the light enters a material with a different dielectric constant and index of refraction, it will experience a change in speed and direction. This is known as refraction. Additionally, the dielectric constant can also affect the absorption of light, leading to changes in the intensity of the light as it passes through the material.

4. What factors can influence the dielectric constant and index of refraction of a material?

The dielectric constant and index of refraction of a material can be influenced by various factors such as temperature, pressure, and the frequency of the electric field. In some cases, the molecular structure and composition of the material can also play a role in determining these properties.

5. Why are dielectric constant and index of refraction important in material science and engineering?

Dielectric constant and index of refraction are important parameters in material science and engineering because they can provide valuable information about the properties and behavior of materials. They are particularly relevant in the design and development of electronic devices, as they can affect the performance and functionality of these devices. Understanding and controlling these properties can also lead to the development of new materials with desired characteristics.

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