Lect28 - Physics 212 Optical Devices Lecture 28 50 40 30 20...

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Unformatted text preview: Physics 212 Optical Devices Lecture 28 50 40 30 20 10 Confused Confident Avg = 3.1 0 Physics 212 Lecture 28, Slide 1 Physics Corny puns and jokes from y’all • • • • What do you do with a dead chemist? (Ans: Barium) i apparently lost my focus for the microscope discussion Have you heard that entropy isn’t what it used to be? YOU MIGHT BE A PHYSICS MAJOR... if you have no life - and you can PROVE it mathematically. if you enjoy pain. if you know vector calculus but you can't remember how to do long division. if you chuckle whenever anyone says "centrifugal force." if you've actually used every single function on your graphing calculator. if it is sunny and 70 degrees outside, and you are working on a computer. if you frequently whistle the theme song to "MacGyver." if you always do physics homework at bars on Friday nights. if you use algebra to determine which coins you need at the laundromat. if you will integrate for food. if you've calculated that the World Series actually diverges. if you hesitate to look at something because you don't want to break down its wave function. if you have a pet named after a scientist. if you laugh at jokes about mathematicians. if the Humane society has you arrested because you actually performed the Schrodinger's Cat experiment. if you can translate English into Binary. if you can't remember what's behind the door in the science building which says "Exit." if you have to bring a jacket with you, in the middle of summer, to enter the lab. if you are completely addicted to caffeine. if you avoid doing anything because you don't want to contribute to the eventual heat-death of the universe. if you consider ANY non-science course "easy." if when your professor asks you where your homework is, you claim to have accidentally determined its momentum so precisely that according to Heisenberg it could be anywhere in the universe. if you'll assume that a horse is a sphere in order to make the math easier. if you understood more than five of these indicators. if you make a hard copy of this list, and post it on your door. 212 Lecture 28, Slide 2 Physics Physics It’s been a pleasure teaching you physics—please come again! Physics 212 Lecture 28, Slide 3 Physics Executive Summary – Mirrors & Lenses: S > 2f 2f 2f > S > f f >S>0 real inverted smaller real inverted bigger virtual upright bigger (converging) concave f converging f 111 += S S′ f S′ M =− S S >0 virtual upright smaller (diverging) convex diverging f f Physics 212 Lecture 28, Slide 4 Physics It’s always the same: 111 += S S′ f S′ M =− S You just have to keep the signs straight: s’ is positive for a real image f is positive when it can produce a real image Lens sign conventions S: S’ : f: S: S’ : f: positive if object is “upstream” of lens positive if image is “downstream” of lens positive if converging lens Mirrors sign conventions positive if object is “upstream” of mirror positive if image is “upstream” of mirror positive if converging mirror (concave) Physics 212 Lecture 28, Slide 5 Physics System of Lenses • Trace rays through lenses, beginning with most upstream lens Image from first lens Becomes object for second lens Physics 212 Lecture 28, Slide 6 Physics System of Lenses • Virtual Objects are Possible !! Object Distance is Negative !! Image from first lens Becomes object for second lens Physics 212 Lecture 28, Slide 7 Physics Normal Eye Physics 212 Lecture 28, Slide 8 Physics Far-sighted Converging Lens creates virtual image at person’s near point Physics 212 Lecture 28, Slide 9 Physics Near-sighted Fix with diverging lens that creates virtual image at far point. Physics 212 Lecture 28, Slide 10 Physics Preflight 2 A B BB Farsighted = Converging Lens Only Converging Lens can produce a REAL IMAGE !! 70 60 50 40 30 20 10 0 Physics 212 Lecture 28, Slide 11 Physics Preflight 4 A B C BB 70 60 50 40 30 20 10 0 θr θi d The image is formed an equal distance BEHIND the mirror Therefore, if you stand a distance = ½ of your near point, the distance to the image will be the near point distance. d Physics 212 Lecture 28, Slide 12 Physics Preflight 6 BB A B C D E 1. Parallel rays are transmitted and pass through focal point (f1) 2. Those rays also pass through focal point of second lens (f2) and therefore are transmitted parallel to the axis. 3. f2 > f1 implies that the width > w1 25 20 15 10 5 0 Physics 212 Lecture 28, Slide 13 Physics The Large Synoptic Survey Telescope Currently being built in Chile. Various members of our Phys Dept are part of the scientific team. Operational in 2015. Particular scientific goals of the LSST include: •Measuring weak gravitational lensing to detect signatures of dark energy and dark matter in the universe. •Mapping near-Earth asteroids •Detecting Novae and supernovae •Mapping the Milky Way Physics 212 Lecture 28, Slide 14 Physics How to make a big telescope mirror Melt it & spin it 52,000 lbs of borosilicate glass when filled Physics 212 Lecture 28, Slide 15 Physics Multiple Lenses Exercises Two converging lenses are set up as shown. The focal length of each lens is 47 cm. The object is a light bulb located 70 cm in front of the first lens. s1=70 cm f=47 cm What is the nature of the image from the first lens alone? (A) REAL UPRIGHT (B) REAL INVERTED (C) VIRTUAL UPRIGHT BB (D) VIRTUAL INVERTED EQUATIONS 111 =− s′ f s s′ = fs s− f PICTURES Draw Rays as above s>f M =− s′ s s’ > 0 M<0 real image inverted image Physics 212 Lecture 28, Slide 16 Physics Multiple Lenses Exercises Two converging lenses are set up as shown. The focal length of each lens is 47 cm. The object is a light bulb located 70 cm in front of the first lens. Lens separation = 2 m What is the object distance s2 for lens 2? (A) s2 = -1.43 m (B) s2 = +1.43 m s1 = 70 cm 70 f = 47 cm s1’ = 1.43 m BB (C) s2 = -0.57 m (D) s2 = +0.57 m (E) s2 = +2.7 m THE OBJECT FOR THE SECOND LENS IS THE IMAGE OF THE FIRST LENS s2 = -0.57 OR s2 = +0.57 Image of first lens is a REAL object for the second lens Physics 212 Lecture 28, Slide 17 Physics Multiple Lenses Exercises Two converging lenses are set up as shown. The focal length of each lens is 47 cm. The object is a light bulb located 70 cm in front of the first lens. Lens separation = 2 m s1=70 cm f=47 cm (A) REAL UPRIGHT (B) REAL INVERTED (C) VIRTUAL UPRIGHT What is the nature of the FINAL image in terms of the ORIGINAL object? s2 = 0.57 m s1’ = 1.43 m BB (D) VIRTUAL INVERTED EQUATIONS s2′ = f s2 s2 − f PICTURES Draw Rays as above s2 > f M2 = − s2′ s2 s2’ > 0 M2 < 0 real image M = M1M2 > 0 upright image RESULTS M = 9.6 s2’ = 2.69 m Physics 212 Lecture 28, Slide 18 Physics Multiple Lenses Exercises Suppose we increase the initial object distance to 74 cm Lens separation = 2 m BB s1=74 cm f=47 cm (A) s2’ increases How does the s2’, the distance to the FINAL image, change? (B) s2’ decreases s2’ : 2.69 m Ø 1.38 m RESULTS s1’ : 1.43 m Ø 1.29 m (C) s2’ remains the same Step through images, one at a time WORDS Increasing s1 will decrease s1’ (moving closer to focal point would increase the image distance) Decreasing s1’ will increase s2 Increasing s2 will decrease s2’ EQUATIONS 111 =− s1′ f s1 1 increases s1′ s2 = 2m − s1′ 1 11 =− s2′ f s2 s2 increases 1 increases s2′ Physics 212 Lecture 28, Slide 19 Physics Multiple Lenses Exercises Suppose we now decrease the initial object distance to 58 cm. Applying the lens equation, we find s1’ = 2.48m Lens separation = 2 m What is the object distance s2 for lens 2? (A) s2 = -0.48 m (B) s2 = +0.48 m s1 = 58 cm 58 f = 47 cm s1’ = 2.48 m BB (C) s2 = -2.48 m (D) s2 = +2.48 m (E) s2 = +2.58 m THE OBJECT FOR THE SECOND LENS IS THE IMAGE OF THE FIRST LENS s2 = -0.48 OR s2 = +0.48 Image of first lens is a VIRTUAL object for the second lens Physics 212 Lecture 28, Slide 20 Physics Multiple Lenses Exercises Suppose we now decrease the initial object distance to 58 cm. Applying the lens equation, we find s1’ = 2.48m Lens separation = 2 m BB s1=58 cm f=47 cm s1’ = 2.48 m s2 = -0.48 m What is the nature of the FINAL image in terms of the ORIGINAL object? (A) REAL UPRIGHT (B) REAL INVERTED (C) VIRTUAL UPRIGHT (D) VIRTUAL INVERTED EQUATIONS s2′ = f s2 s2 − f PICTURES Draw Rays as above s2 < 0 M2 = − s2′ s2 s2’ > 0 M2 > 0 real image M = M1M2 < 0 inverted image RESULTS M = -2.1 s2’ = 0.24 m Physics 212 Lecture 28, Slide 21 Physics ...
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This note was uploaded on 02/21/2011 for the course PHYS 212 taught by Professor Kim during the Spring '08 term at University of Illinois, Urbana Champaign.

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