# Explain the value of refractive index of water?

• Yen Pham
In summary, the conversation discusses the formula for refractive index and its application to water. The formula states that for water with a relative permittivity of 81 and a value of 1 for μ, the refractive index should be 9. However, it is often observed that the value of 1.33 is used instead. The reason for this is that the relative permittivity and refractive index change with frequency, making the chosen value of 81 invalid for visible wavelengths. This is clarified by another participant in the conversation.
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!

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.

Yen Pham
Orodruin said:
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.
yeah, I got it! Thank you so much^^

## 1. What is refractive index and how is it related to water?

Refractive index is a measure of how much a material, such as water, can bend or refract light. It is related to water because water has a specific refractive index value that is used to measure the speed of light passing through it.

## 2. What is the importance of knowing the refractive index of water?

Knowing the refractive index of water is important in many scientific and practical applications. It is used in fields such as optics, chemistry, and biology to determine the concentration, purity, and properties of substances dissolved in water. It is also crucial in determining the quality of water for drinking or industrial purposes.

## 3. How is the refractive index of water measured?

The refractive index of water is typically measured using a device called a refractometer. This instrument measures the bending of light as it passes through a sample of water and calculates the refractive index based on this measurement. Other methods such as using spectrometers or calculating the index from known physical properties of water can also be used.

## 4. How does the refractive index of water change with temperature?

The refractive index of water is temperature-dependent, meaning it changes as the temperature of the water changes. This is because the speed of light passing through water is affected by temperature. As the temperature increases, the refractive index decreases, and vice versa.

## 5. Why is the refractive index of water different from other liquids?

The refractive index of water is different from other liquids because it has a unique molecular structure that allows light to pass through it more easily. Water molecules are highly polar, meaning they have a positive and negative end, which allows them to interact with light in a specific way. This results in a different refractive index compared to other liquids with different molecular structures.

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