# Critical angle

1. Jun 5, 2015

### 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.

2. Jun 5, 2015

### blue_leaf77

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?

3. Jun 5, 2015

### Samurai44

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

4. Jun 5, 2015

### blue_leaf77

If you had known this, then why would you get sine inverse greater than one when calculating a critical angle?