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# Lect15 - Total Internal Reflection Lecture 15 Light Snells...

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1 Lecture 15: Light Refraction Total Internal Reflection Fiber Optics Dispersion Rainbow Prizms Spherical Mirrors October 11 Physics 104, Fall 2011 1 October 11 Physics 104, Fall 2011 2 Total Internal Reflection normal θ 2 θ 1 n 2 n 1 Snell’s Law: n 1 sin( θ 1 )= n 2 sin( θ 2 ) when n 1 > n 2 , θ 2 > θ 1 When θ 1 = sin -1 (n 2 /n 1 ) θ 2 = 90 0 θ c This is critical angle θ i θ r Light incident at a larger angle will be completely reflected θ i = θ r October 11 Physics 104, Fall 2011 3 Can the person standing on the edge of the pool be prevented from seeing the light by total internal reflection ? 1) Yes 2) No Reading Quiz Java Rays coming from above the straight through line will not reflect in, but there are other rays that make it to the eye! Question As we pour more water into bucket, what will happen to the number of people who can see the ball? 1) Increase 2) Same 3) Decrease October 11 Physics 104, Fall 2011 4 Fiber Optics October 11 Physics 104, Fall 2011 5 At each contact with the glass air interface, if the light hits at greater than the critical angle, it undergoes total internal reflection and stays in the fiber. Telecommunications Endoscopy Reading Quiz Which of the following statements is true given the ray diagram below illustrating cross section of a optical fiber? – n Cladding < n Core – n Cladding = n Core – n Cladding > n Core October 11 Physics 104, Fall 2011 6

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2 Reading Quiz If by accident the refractive indices of core and cladding are swapped, which of the following statements is true for the light incident at the same angle theta to the normal to the cladding surface? – Internally reflected ray remains at the same angle – Internally reflected ray disappears – Internally reflected ray remains but at a different angle – Some light will be partially refracted into the cladding October 11 Physics 104, Fall 2011 7 Reading Quiz The critical angle of a glass block is its intrinsic property, and remains the constant as long as the block is not physically damaged. Is this statement true? – Yes – No October 11 Physics 104, Fall 2011 8 If the same glass block is put in water its critical angle would be different - θ c depends on the refractive indices of the two media at the interface. Reading Quiz In the above picture, if the angle theta, made by the ray and the normal to the cladding surface, is varied. Which of the following statements are true? The angle of internally reﬂected ray is always equal to theta. The intensity of internally reﬂected ray remains constant. The intensity of internally reﬂected ray varies. At some angle light is [email protected] refracted into the cladding. If any light is refracted into the cladding it makes an angle larger than theta to the normal. If any light is refracted into the cladding it makes an angle smaller than theta to the normal.
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Lect15 - Total Internal Reflection Lecture 15 Light Snells...

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