Ray of light travels from an optically denser medium

In summary, when a ray of light travels from an optically denser medium to a rarer one at the critical angle, the refracted ray will graze the interface. The principle of reversibility of light does work in this case, but the corresponding evanescent wave cannot be formed with an ordinary source of light. This is because the evanescent wave is not space-propagating, so it cannot be directed at the interface to launch a planewave at the critical angle. This also means that the evanescent wave does not correspond with Snell's law. The critical angle from a light medium to a denser medium can be calculated using Snell's law, but this does not mean that a vertical beam will
  • #1
Rainbow
62
0
When a ray of light travels from an optically denser medium to a rarer one such that the angle of incidence equals the critical angle, then the refracted ray grazes the interface.

Now, will the principle of reversibility of light work in this case? If yes, please explain.
 
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  • #2
Does Snell's law depend on direction?
 
  • #3
Yes, it is reversible.

But the corresponding evansecent wave is somthing that you cannot form
with an ordinary source of light. If you could, you could launch a planewave
into the denser medium at the critical angle.
 
  • #4
Antiphon said:
Yes, it is reversible.

But the corresponding evansecent wave is somthing that you cannot form
with an ordinary source of light.
why is that?
 
  • #5
loop quantum gravity said:
why is that?

The evanescent wave is not space-propagating. So there is no way to
form a planewave of (space-propagating) light which could be directed at the interface from
the low-index side and result in the right surface fields needed to launch
the planewave at the critical angle into the dense medium.
 
Last edited:
  • #6
but surely it doenst correspond with snell's law.

if we have n1=1 and n2=1.33
then the critical angle from a light medium (n1) to a denser medium (n2) is
a_cr=arcsin(n2/n1)=arcsin(1.33) and needless to remind you the limits of sin function.
 
  • #7
But you are not "running it in reverse". As light goes from a lighter medium to a heavier (higher speed of light in the medium to lower), the "critical angle" is the incoming angle at which the outgoing angle is 90 degrees. That does not mean that, going the other way, a vertical beam will leave at the "critical angle". A vertical beam will leave vertically.
 

What is meant by "optically denser medium"?

An optically denser medium refers to a material or substance that has a higher refractive index than the surrounding medium. This means that light traveling through the denser medium will slow down and change direction.

How does light travel through an optically denser medium?

When light enters an optically denser medium, it slows down and changes direction due to the change in refractive index. This is known as refraction. The amount of refraction depends on the angle at which the light enters the medium and the difference in refractive index between the two mediums.

What happens when light travels from an optically denser medium to an optically less dense medium?

When light travels from an optically denser medium to an optically less dense medium, it speeds up and changes direction again. This is known as refraction. The amount of refraction depends on the angle at which the light enters the medium and the difference in refractive index between the two mediums.

What is the law of refraction?

The law of refraction, also known as Snell's law, states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the refractive indices of the two mediums. In other words, it describes the relationship between the angle of incidence and the angle of refraction when light travels from one medium to another.

How does the speed of light change when it travels from an optically denser medium to an optically less dense medium?

The speed of light decreases when it travels from an optically denser medium to an optically less dense medium, and increases when it travels from an optically less dense medium to an optically denser medium. This is due to the change in refractive index and is described by the law of refraction.

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