Physics 102: Lecture 18, Slide 1 Total Internal Reflection, Brewster’s Angle, Dispersion, Lenses Today’s Lecture will cover textbook sections , 9 Physics 102: Lecture 18

Physics 102: Lecture 18, Slide 2 Total Internal Reflection normal 22 11 n2n2 n1n1 Recall Snell’s Law: n 1 sin(  1 )= n 2 sin(  2 ) (n 1 > n 2   2 >  1 )  1 = sin -1 (n 2 /n 1 ) then  2 = 90 cc Light incident at a larger angle will only have reflection (  i =  r ) ii rr “critical angle”

Physics 102: Lecture 18, Slide 3 Can the person standing on the edge of the pool be prevented from seeing the light by total internal reflection ? 1) Yes2) No Preflight 18.1

Physics 102: Lecture 18, Slide 4 Can the person standing on the edge of the pool be prevented from seeing the light by total internal reflection ? 1) Yes2) No Preflight 18.1 Java

Physics 102: Lecture 18, Slide 5 ACT: Refraction As we pour more water into bucket, what will happen to the number of people who can see the ball? 1) Increase2) Same3) Decrease

Physics 102: Lecture 18, Slide 6 ACT: Refraction As we pour more water into bucket, what will happen to the number of people who can see the ball? 1) Increase2) Same3) Decrease

Physics 102: Lecture 18, Slide 7 ACT: Refraction As we pour more water into bucket, what will happen to the number of people who can see the ball? 1) Increase2) Same3) Decrease

Physics 102: Lecture 18, Slide 8 Fiber Optics Telecommunications Arthroscopy Laser surgery Total Internal Reflection only works if n outside < n inside At each contact w/ the glass air interface, if the light hits at greater than the critical angle, it undergoes total internal reflection and stays in the fiber. n inside n outside

Physics 102: Lecture 18, Slide 9 Fiber Optics At each contact w/ the glass air interface, if the light hits at greater than the critical angle, it undergoes total internal reflection and stays in the fiber. We can be certain that n cladding < n inside n inside Add “cladding” so outside material doesn’t matter! n cladding n outside

Physics 102: Lecture 18, Slide 10 Brewster’s angle …when angle between reflected beam and refracted beam is exactly 90 degrees, reflected beam is 100% horizontally polarized ! Reflected light is partially polarized (more horizontal than vertical). But… horiz. and vert. polarized BB BB 90º-  B 90º horiz. polarized only! n1n1 n2n2 tan θ B =

Physics 102: Lecture 18, Slide 11 Brewster’s angle …when angle between reflected beam and refracted beam is exactly 90 degrees, reflected beam is 100% horizontally polarized ! Reflected light is partially polarized (more horizontal than vertical). But… n 1 sin  B = n 2 sin (90-  B ) n 1 sin  B = n 2 cos (  B ) horiz. and vert. polarized BB BB 90º-  B 90º horiz. polarized only! n1n1 n2n2

Physics 102: Lecture 18, Slide 12 Polarizing sunglasses are often considered to be better than tinted glasses because they… Preflight 18.3, 18.4 block more light block more glare are safer for your eyes are cheaper Polarizing sunglasses (when worn by someone standing up) work by absorbing light polarized in which direction? horizontal vertical

Physics 102: Lecture 18, Slide 13 Polarizing sunglasses are often considered to be better than tinted glasses because they… Preflight 18.3, 18.4 block more light block more glare are safer for your eyes are cheaper When glare is around  B, it’s mostly horiz. polarized! Polarizing sunglasses (when worn by someone standing up) work by absorbing light polarized in which direction? horizontal vertical

Physics 102: Lecture 18, Slide 14 ACT: Brewster’s Angle When a polarizer is placed between the light source and the surface with transmission axis aligned as shown, the intensity of the reflected light: (1) Increases(2) Unchanged(3) Decreases T.A.

Physics 102: Lecture 18, Slide 15 ACT: Brewster’s Angle When a polarizer is placed between the light source and the surface with transmission axis aligned as shown, the intensity of the reflected light: (1) Increases(2) Unchanged(3) Decreases T.A.

Physics 102: Lecture 18, Slide 16 Dispersion prism White light Blue light gets deflected more n blue > n red The index of refraction n depends on color! In glass: n blue = 1.53n red = 1.52

Physics 102: Lecture 18, Slide 17 Preflight 18.5 Wow look at the variation in index of refraction! Which is red? Which is blue? (1) (2)

Physics 102: Lecture 18, Slide 18 Skier sees blue coming up from the bottom (1), and red coming down from the top (2) of the rainbow. Preflight 18.5 Wow look at the variation in index of refraction! Which is red? Which is blue? Blue light is deflected more!

Physics 102: Lecture 18, Slide 19 LIKE SO!In second rainbow pattern is reversed

Physics 102: Lecture 18, Slide 20 Flat Lens (Window) n1n1 n2n2 Incident ray is displaced, but its direction is not changed. tt 11 11 If  1 is not large, and if t is small, the displacement, d, will be quite small. d

Physics 102: Lecture 18, Slide 21 Converging Lens All rays parallel to principal axis pass through focal point F. Double Convex P.A. F Preflight 18.6 A beacon in a lighthouse produces a parallel beam of light. The beacon consists of a bulb and a converging lens. Where should the bulb be placed? n lens > n outside F At F Inside F Outside F P.A. F

Physics 102: Lecture 18, Slide 22 Converging Lens All rays parallel to principal axis pass through focal point F. Double Convex P.A. F Preflight 18.6 A beacon in a lighthouse produces a parallel beam of light. The beacon consists of a bulb and a converging lens. Where should the bulb be placed? n lens > n outside F At F Inside F Outside F P.A. F F

Physics 102: Lecture 18, Slide 23 1) Rays parallel to principal axis pass through focal point. 2) Rays through center of lens are not refracted. 3) Rays through F emerge parallel to principal axis. Assumptions: monochromatic light incident on a thin lens. rays are all “near” the principal axis. Converging Lens Principal Rays F F Object P.A. Image is (in this case): Real orImaginary Inverted or Upright Enlarged or Reduced

Physics 102: Lecture 18, Slide 24 1) Rays parallel to principal axis pass through focal point. 2) Rays through center of lens are not refracted. 3) Rays through F emerge parallel to principal axis. Assumptions: monochromatic light incident on a thin lens. rays are all “near” the principal axis. Converging Lens Principal Rays F F Object P.A. Image is: real, inverted and enlarged (in this case). Image

Physics 102: Lecture 18, Slide 25 ACT: Converging Lens Which way should you move object so image is real and diminished? (1)Closer to lens (2)Further from lens (3)Converging lens can’t create real diminished image. F F Object P.A.

Physics 102: Lecture 18, Slide 26 ACT: Converging Lens Which way should you move object so image is real and diminished? (1)Closer to lens (2)Further from lens (3)Converging lens can’t create real diminished image. Demo F F Object P.A.

Physics 102: Lecture 18, Slide 27 ImageObject Image Object Image 3 Cases for Converging Lenses This could be used as a projector. Small slide on big screen This is a magnifying glass This could be used in a camera. Big object on small film Upright Enlarged Virtual Inverted Enlarged Real Inverted Reduced Real Inside F Past 2F Between F & 2F

Physics 102: Lecture 18, Slide 28 1) Rays parallel to principal axis pass through focal point. 2) Rays through center of lens are not refracted. 3) Rays toward F emerge parallel to principal axis. Diverging Lens Principal Rays F F Object P.A. Image is (always true): Real or Imaginary Upright or Inverted Reduced or Enlarged

Physics 102: Lecture 18, Slide 29 1) Rays parallel to principal axis pass through focal point. 2) Rays through center of lens are not refracted. 3) Rays toward F emerge parallel to principal axis. Diverging Lens Principal Rays F F Object P.A. Image is virtual, upright and reduced. Image

Physics 102: Lecture 18, Slide 30 Which way should you move object so image is real? 1)Closer to lens 2)Further from lens 3)Diverging lens can’t create real image. ACT: Diverging Lenses F F Object P.A.

Physics 102: Lecture 18, Slide 31 Which way should you move object so image is real? 1)Closer to lens 2)Further from lens 3)Diverging lens can’t create real image. ACT: Diverging Lenses Demo F F Object P.A.

Physics 102: Lecture 18, Slide 32 See you next class! Read Sections 23.9, 24.1, 3-4, 6