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After a light ray gets refracted at the boundary of a refracting medium, why do sent the light ray keep refracting inside. Cause if you divide the medium into many boundary layers then light should keep refracting inside. There is no way each layer in the medium can know that refracred ray has already been refracted. So the light ray must bend. Please bring out the fundamental flaw in this question.

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  • $\begingroup$ Should at least one of those "refract" occurrences be "reflect"? I'm having trouble understanding the question. When a light ray gets refracted at the boundary of a medium, the refracted ray leaves the medium - it doesn't keep "refracting inside". However, the reflected ray does stay inside the medium. Is that what you're asking about? $\endgroup$ – Brionius Dec 22 '15 at 13:05
  • $\begingroup$ In general, it would help if you'd carefully proofread your question - for instance, if you read the title carefully, you wrote "refraction inside a retracting medium". There are other errors too, and it's not as obvious what you meant by some of them. $\endgroup$ – Brionius Dec 22 '15 at 13:06
  • $\begingroup$ What I meant is why dosent light keep refracting inside the second medium can't we divide the medium into individual layers, light should keep refracting as refraction is a boundary phenomenon $\endgroup$ – N.S.JOHN Dec 22 '15 at 13:12
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If I understand your question correctly, the answer is the light does keep refracting inside the second medium. Let me explain what I mean:

Let's, as you suggest, divide the second medium into layers. Assuming the medium is homogeneous, the index of refraction of each layer is the same! They're all made of the same material.

So, if we apply Snell's Law of Refraction:

$$n_1 \sin(\theta_1) = n_2 \sin(\theta_2)$$

But $n_1 = n_2$ for every one of our layers: $$n_1 \sin(\theta_1) = n_1 \sin(\theta_2)$$ $$\sin(\theta_1) = \sin(\theta_2)$$ $$\theta_1 = \theta_2$$

So what do we conclude? That for each of the layers we've divided our medium up into, the angle of incidence is the same as the angle of refraction. What does that look like? A straight line!

So yes, in a sense, the light beam is continuously refracting. However, you only see a change in direction of the light beam when the index of refraction changes, for example at a boundary between two different media.

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  • $\begingroup$ Can u please explain the derivation for snells law then .that would really clear my doubts $\endgroup$ – N.S.JOHN Dec 22 '15 at 13:24
  • $\begingroup$ There are multiple ways to derive Snell's law, but that's really a separate question that you could ask. The derivation is available in Wikipedia here: Snell's law: Derivations and Formula $\endgroup$ – Brionius Dec 22 '15 at 13:27

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