# Calculating Critical Angle: Relative vs. Absolute Refractive Index

• Samurai44
In summary, the conversation is about finding the critical angle using Snell's law and how to calculate it when dealing with two mediums that are not vacuum or air. The requirement for total internal reflection to occur is also discussed. The conversation also mentions the confusion that can arise when finding the relative refractive index and the fact that critical angle only occurs from denser to less dense mediums.
Samurai44
Greetings,
Do we use Absloute refractive index when finding crtical angle ?

if it was two mediums ( not vacuum or air) how would i calculate the critical angle ? I mean i get confused when I find relative refractive index because sometimes i get sine inverse greater than 1 which give no solution .

Thank you in advance.

Snell's law reads as ##n_1 \sin{\theta_1} = n_2 \sin{\theta_2} ##. Now if we assume ##n_1## to be greater than ##n_2## and ##\theta_2 = 90^0##, what will you end up with?
What can you then conclude for the requirement for ##n_1## and ##n_2## so that total internal reflection which is associated with critical angle can take place?

blue_leaf77 said:
Snell's law reads as ##n_1 \sin{\theta_1} = n_2 \sin{\theta_2} ##. Now if we assume ##n_1## to be greater than ##n_2## and ##\theta_2 = 90^0##, what will you end up with?
What can you then conclude for the requirement for ##n_1## and ##n_2## so that total internal reflection which is associated with critical angle can take place?

it will end up with ##n_1 \sin{\theta_1} = n_2 ? , n1 is denser than n2 since its greater than
I know the fact that critical angle occurs only from denser medium to less dense , and that's why I get confused when I find relative refractive index

Samurai44 said:
I know the fact that critical angle occurs only from denser medium to less dense ,
If you had known this, then why would you get sine inverse greater than one when calculating a critical angle?

## 1. What is the critical angle?

The critical angle is the angle of incidence at which light passing through a boundary between two different mediums will be refracted at an angle of 90 degrees.

## 2. How is the critical angle calculated?

The critical angle can be calculated using the formula: θc = sin^-1(n2/n1), where θc is the critical angle, n1 is the refractive index of the first medium, and n2 is the refractive index of the second medium.

## 3. What is the difference between relative and absolute refractive index?

The relative refractive index is the ratio of the speed of light in a vacuum to the speed of light in a specific medium, while the absolute refractive index is the speed of light in a specific medium compared to the speed of light in a vacuum.

## 4. How do relative and absolute refractive index affect the critical angle?

The critical angle is determined by the ratio of the refractive indices of the two mediums. A higher relative refractive index or a lower absolute refractive index will result in a smaller critical angle, meaning light will be more easily refracted.

## 5. What are some real-life applications of calculating critical angle?

Calculating critical angle is important in understanding the behavior of light in various mediums, which has many practical uses. Some examples include fiber optic communication, underwater photography, and the design of lenses in cameras and telescopes.

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