# "Critical" in reflected and refracted rays

Hello,

I didnt understand what the "critical" in critical rays are. I didnt understand the meaning.

Thanks.

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nrqed
Homework Helper
Gold Member
Hello,

I didnt understand what the "critical" in critical rays are. I didnt understand the meaning.
Hard to tell without more context. I assume you are talking about critical angles, for total internal reflection (ray coming from side 1 and $n_1>n_2$)? This is when the angle of refraction reaches 90 degrees and pretty much all the energy is reflected inside the material (I assume n1 > n2). Then we have $theta_2=90$ and you can find the critical angle inside the medium.