Lab 9: Reflection and Refraction –Law of Reflection –Law of Refraction (Snell’s Law) 1.Index of Refraction 2.The Critical Angle 3.Total Internal Reflection 4.Dispersion 5.Light Passing through a Window Pane or Prism 6.How Large does a Mirror Need to be? 7.Location of Mirror Image 8.Rainbows 9.Corner Reflectors 10.Fiber Optics 11.Polarization by Reflection

Light ray –Originates at a point source –Travels straight –Changes direction at interface Reflection & refraction in this lab Object –Point source of light rays Image –Apparent convergence point of light rays from object

Draw diagrams involving –Light rays –Interface –Angles Estimate angles to the tenth of a degree –Take several measurements and then average them

Light Rays indicated as arrows from object  extend outward

Light Rays light unit: a ray of light made by a slit white light

Interface Cross-sectional View medium air interface : boundary between different media normal : direction perpendicular to interface

Reflection (Specular) Cross-sectional View mirror air ii angle of incidence (  i ) rr angle of reflection (  r ) angles measured from normal

Top view Aim light ray at the center of semicircle. AA ray of light MM Experiment #1 AA MM ray of light Experiment #2 Component Line

 A (degree)  M (degree) sin  A sin  M sin  A /sin  M (= n glass ) 0N/A 10  85 Use the “degree” mode on your calculator  i (degree)  r (degree)  r –  i (degree) 0 10  85 Reflection Refraction #1

Lab 9: Reflection and Refraction –Law of Reflection –Law of Refraction (Snell’s Law) 1.Index of Refraction 2.The Critical Angle 3.Total Internal Reflection 4.Dispersion 5.Light Passing through a Window Pane or Prism 6.How Large does a Mirror Need to be? 7.Location of Mirror Image 8.Rainbows 9.Corner Reflectors 10.Fiber Optics 11.Polarization by Reflection

Specular Reflection  i (degree)  r (degree)  r –  i (degree) %error  r –  i )/  i 0N/A 10  85 Reflection Use the “degree” mode on your calculator

Mirror Side view You want to see your entire image. 1.Minimum length of the mirror? 2.Where should bottom and top of mirror be?

Mirror Top view 1 m Where do light rays appear to come from?

Corner Reflectors Top view ii Normal  corner You want incident and reflected rays to be parallel. 1.Reflection angles? 2.What should  corner be? Caution: LASER!

Polarization by Reflection Look through the polarizer while turning it slowly. Any changes? Path of light rays? How can you eliminate the specular reflection of light bulb off the glass plate?

Lab 9: Reflection and Refraction –Law of Reflection –Law of Refraction (Snell’s Law) 1.Index of Refraction 2.The Critical Angle 3.Total Internal Reflection 4.Dispersion 5.Light Passing through a Window Pane or Prism 6.How Large does a Mirror Need to be? 7.Location of Mirror Image 8.Rainbows 9.Corner Reflectors 10.Fiber Optics 11.Polarization by Reflection

Refraction air interface water aa angle of incidence mm angle of refraction mm angle of incidence aa angle of refraction Index of RefractionSnell’s Law

Critical Angle -  c denser less dense  m smaller than  c mm cc aa  m equal to  c  a = 90   m =  c  m beyond  c mm cc

1. Index of Refraction  A (degree)  M (degree) sin  A sin  M sin  A /sin  M (= n glass ) 0N/A 10  85 Use the “degree” mode on your calculator Refraction Experiment 1

Dispersion Top view MM White light What color of light is bent more by refraction? Which is larger, n Red or n Blue ? How do you show that?

Pane of Glass – Parallel Interface Top view How does a light ray go through and come out from a pane of glass? How are angles inside and out side of glass related to  A ? How large is the deviation angle? AA

Rainbows Read the rainbow section of online textbook Write a short summary of the part you liked most – in a few sentences

Fiber Optics Top view How does a light ray travel through the fiber? How do you know if it is total internal reflection? Does the ray refract out of the fiber? From side wall?

Answers Never show the following slides to students!!!

Mirror Top view 1 m

Mirror Side view 2 m

Mirror Side view ii rr Color coded right triangles have the same adjacent sides also  i =  r  congruent The ray from foot is reflected at half way between foot and eye h h

Corner Reflectors Top view ii rr rr  i =  r by Law of Reflection Normal rr

1. Index of Refraction  A (degree)  M (degree) sin  A sin  M sin  A /sin  M 0N/A 5~ ~1.50  89~1.50 In good measurements, n is usually 1.50 ± 0.01 for plexiglass

Dispersion Top view  Red MM White light Blue Red  Blue So n Blue is larger

Pane of Glass Top view  A’ =  A  M’ =  M AA MM Apply Snell’s law at each interface. No deflection across the pane of glass occurs. But the incident and the refracted rays are shifted spatially. t

Fiber Optics Top view Does it refract into the surrounding air? No since there is no intense rays coming out Can you see any light from side wall? Scattered light – yes.

Problems - Refraction apparent position real position rays appear to come from apparent position

apparent position real position rays from three different locations