# Explain the value of refractive index of water?

1. Jan 30, 2016

### Yen Pham

I have studied about the formula of refractive index which is: . That means in the case of water which have μ =1 (approximate) and ε = 81, then n should be 9. But why we often use the value n = 1.33 for water ???
Who can explain for me? I don't think the above formula is wrong, of course!

2. Jan 30, 2016

### Orodruin

Staff Emeritus
You have taken a value for the relative permittivity which is not valid for visible wavelengths. The permittivity (and hence refractive index) changes with the frequency.

3. Jan 30, 2016

### Yen Pham

yeah, I got it! Thank you so much^^