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April 29, 2024, 09:40:29 pm
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Author Topic: Yr 11 Light Q Help?  (Read 961 times)  Share 

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Andiio

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Yr 11 Light Q Help?
« on: October 19, 2010, 09:15:25 pm »
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A ray travelling through water (n = 1.33) approaches the surface at an angle of incidence of 55 degrees. What will happen to the ray? Support your answer with calculations.

Does the ray undergo total internal reflection instead? As n1 > n2?
:/
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sxcalexc

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Re: Yr 11 Light Q Help?
« Reply #1 on: October 19, 2010, 09:33:39 pm »
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Travelling from an optically denser to a less dense medium will just mean that it will refract and bend away from the normal.

Total internal reflection is a special condition that occurs for angles greater than arcsin(n2/n1) i.e. > ~49 degrees in this case.

Since 55 degrees is above this critical angle, it will indeed totally internally reflect and no light will pass through.
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Andiio

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Re: Yr 11 Light Q Help?
« Reply #2 on: October 19, 2010, 09:51:40 pm »
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Oh okay, thanks!

What about this question?Calculate the angle of deviation at a glass-air interface for an angle of incidence of 65 degrees and refractive index of glass of 1.55.
Wouldn't T.I.R. occur here as well? How would you find the refracted angle then? :/
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kyzoo

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Re: Yr 11 Light Q Help?
« Reply #3 on: October 19, 2010, 10:09:54 pm »
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hahaha this stuff has totally escaped my mind
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Andiio

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Re: Yr 11 Light Q Help?
« Reply #4 on: October 19, 2010, 10:12:25 pm »
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Argh it's just that my textbook is SO BAD. 99.95% of the questions' answers are all wrong, and aohrfaoyyt1896251285r6P@&*"P%&QY*HFOV
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sxcalexc

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Re: Yr 11 Light Q Help?
« Reply #5 on: October 19, 2010, 10:28:50 pm »
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Quote from: Andiio on October 19, 2010, 09:51:40 pm
Oh okay, thanks!

What about this question?Calculate the angle of deviation at a glass-air interface for an angle of incidence of 65 degrees and refractive index of glass of 1.55.
Wouldn't T.I.R. occur here as well? How would you find the refracted angle then? :/

Yeah... it would. They do say glass-air interface, does that imply that light is travelling from glass to air? I would use deduction and say that because they're asking for an angle of deviation they mean light travelling from the air to glass. Underspecified question, that is.
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Andiio

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Re: Yr 11 Light Q Help?
« Reply #6 on: October 19, 2010, 10:32:21 pm »
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Yeah, so you can't really find the angle of deviation can you? Sigh this book is so bad. -.-
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sxcalexc

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Re: Yr 11 Light Q Help?
« Reply #7 on: October 19, 2010, 10:53:59 pm »
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Well you can find the angle of deviation if it's from air to glass because then total internal reflection won't occur. So if you construe it as air to glass, you can find an answer.

If you construe it the other way you can't. (or it's a trick/bad question or something)
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Andiio

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Re: Yr 11 Light Q Help?
« Reply #8 on: October 19, 2010, 10:58:52 pm »
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Mmm that's what I thought as well; the question clearly states the glass to air interface though.. sigh!
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MBBS

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Re: Yr 11 Light Q Help?
« Reply #9 on: October 20, 2010, 02:19:51 pm »
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I remember not being able to do this question and my father did it for me, he said don't stress as it's not something he expects would be asked on an exam.
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