# Dielectric constant refractive index relationship

1. Dec 20, 2011

### tomas632

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

2. Dec 20, 2011

### Simon Bridge

3. Dec 20, 2011

### nasu

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).

4. Dec 22, 2011

### drhassan

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)