Is the Book Wrong About Total Internal Reflection and Snell's Law?

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Homework Help Overview

The discussion revolves around the concepts of total internal reflection and Snell's Law, particularly focusing on the relationship between angles of incidence and refraction, as well as the behavior of light as it transitions between different media.

Discussion Character

  • Conceptual clarification, Assumption checking, Mixed

Approaches and Questions Raised

  • Participants explore the relationship between the angle of incidence and the angle of refraction, questioning whether the angle of refraction increases or decreases with increasing incidence. There are inquiries about the implications of Snell's Law when the indices of refraction differ. Additionally, questions arise regarding the constancy of frequency when light transitions between media and how speed, frequency, and wavelength interrelate.

Discussion Status

Some participants express confusion about the application of Snell's Law and the behavior of light in different media. Others provide insights into the constancy of frequency and the relationship between speed and wavelength, suggesting that further exploration of these concepts may clarify misunderstandings. The discussion remains open with various interpretations being considered.

Contextual Notes

Participants are grappling with potential misconceptions from a textbook and are seeking clarification on fundamental principles of optics. There is a noted lack of consensus on certain points, particularly regarding the behavior of angles and the implications of refractive indices.

AznBoi
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As the angle of incidence increases, the angle of refraction becomes larger.

Should the underlined word be decreases? why? I think I've found a mistake in the book because according to snell's law of refraction n1sin(theta)1=n2 sin(theta)2 right? If n1>n2 then (theta)1<(theta)2

Wait, I don't know now. I think I'm getting mixed up with angles and indices. =[ Help please.
 
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Is there any easy way to remember the relation of n=c/v, snails law, and how the refracted angle behaves when n1>n2 or vice versa?
 
Also, how come the frequency of light doesn't change as is passes from one medium to another? How do you know if the speed of the wave, frequency, or wavelength changes? I know that the speed of sound/light changes when it goes through another medium but how do you know if frequency or wavelength change or stays constant? Is there a rule for this concept? Thanks
 
bump. help anyone please?
 
AznBoi said:
As the angle of incidence increases, the angle of refraction becomes larger.

Should the underlined word be decreases? why? I think I've found a mistake in the book because according to snell's law of refraction n1sin(theta)1=n2 sin(theta)2 right? If n1>n2 then (theta)1<(theta)2

Wait, I don't know now. I think I'm getting mixed up with angles and indices. =[ Help please.


The book is correct. The angle of the refracted ray will bend away from the normal for increasing values of incident angle, in both cases of n1>n2 and n1<n2. Perhaps work out a table of values to see for yourself.
 
I will try to explain this, as I learned it. Maybe someone can fill it in a bit.
If you think of the wave fronts being parallel to the boundary between the two media, the number of wave fronts (so frequency) passing a point in medium 1 must be the same as the number of wave fronts passing a point in medium 2. If this were not true, wave fronts would be piling up or being destroyed or whatever and there is no physical mechanism for that to happen. So since the speed changes, the wavelength must change, to keep the relation of velocity = frequency*wavelength valid (in both media).

Hopefully that helps a bit.
 

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