Faced total internal reflection in real life

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Once upon a winter morning

The seat you can see to my left in the above picture doesn’t actually exist, it is just a formed image. Is that a mirror then, beside me? No, it’s just a normal glass, the type of normal glass used in a low-class bus (sort of a vehicle). Well, what happened here?

The phenomenon that took place here is total internal reflection. I sat on a seat, the rear seat is visible here through a total internal reflection. The thing is, light rays from that seat fell on the glass beside me with an angle greater than the critical angle of the glass w.r.t. air. This is why total internal reflection took place here.

What is critical angle?

We know that when a light ray leaves an optically denser medium to enter a lighter one the ray strays from the ‘Normal’ on the point of incidence on the plane separating the two media. Then there must be a value of incident angle for which the refraction angle will be 90 degrees. In such a case the refracted ray will pass along the aforementioned plane. This value of incident angle is called the critical angle of the denser medium w.r.t. the lighter medium.

What is Total Internal Reflection?

When light rays coming from an optically denser medium attempt to pass through a lighter medium with an incident angle greater than the critical angle of the two media, NO refraction takes place here. Instead all the light rays get reflected in the denser medium, obeying the rules of reflection. This incident is called total internal reflection. It is better than normal reflection. That’s because in normal reflection 40%-50% of light gets reflected and in total internal reflection 100% light gets reflected. As a result, an image formed due to the latter type of reflection looks very bright.

Color of light is considerable

Critical angle and total internal reflection depend on which chrome of light is used. The value of the angle also depends on which two media are considered. Generally speaking, critical angle has a greater value for violet light than red light. Because when changing media violet light bends more than red light.


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