Slide 1RefractionSlide 3Slide 4Slide 5A material has an index of refraction that increases continuously from top to bottom. Of the three paths shown in the figure below, which path will a light ray follow as it passes through the material?DispersionVariation of Index of Refraction with WavelengthRefraction in a PrismPrism SpectrometerUsing Spectra to Identify GasesTotal Internal ReflectionCritical AngleChapter 23 Light :Geometric OpticsSlide 15Slide 16Slide 17Slide 18A plastic sandwich bag filled with water can act as a crude converging lens in air. If the bag is filled with air and placed under water, is the effective lens (a) converging or (b) diverging?(b). In this case, the index of refraction of the lens material is less than that of the surrounding medium. Under these conditions, a biconvex lens will be divergent.The Lens EquationSlide 22An object is placed to the left of a converging lens. Which of the following statements are true and which are false? (a) The image is always to the right of the lens. (b) The image can be upright or inverted. (c) The image is always smaller or the same size as the object. Justify your answers with ray diagrams.(a) False. A virtual image is formed on the left side of the lens if do < f. (b) True. An upright, virtual image is formed when do < f, while an inverted, real image is formed when do > f. (c) False. A magnified, real image is formed if 2f > do > f, and a magnified, virtual image is formed if do > f.Slide 25Slide 26Slide 27Slide 28Slide 29Sign Conventions for LensesSlide 31Slide 32Slide 33Slide 34Slide 351/do+1/di=1/f=2/r m=hi/ho=- di/dododiSpherical MirrorRefraction•Refraction refers to the bending of a light ray when it goes from one medium to another•Refraction occurs because light travels at different speeds in different mediaIndex of Refraction n=c/v where c is the speed of the light in vacuum (3x108 m/s), and v the speed in a given materialSnell’s Law n1sini =n2sinrOr sini /sinr =v1/v2Question: When you look down into a swimming pool, are you likely to underestimate or overestimate its depth? Answer: The pool appears shallower than it is.QUICK QUIZ 22.3A material has an index of refraction that increases continuously from top to bottom. Of the three paths shown in the figure below, which path will a light ray follow as it passes through the material?Dispersion•The index of refraction in anything except a vacuum depends on the wavelength of the light•This dependence of n on λ is called dispersion•Snell’s Law indicates that the angle of refraction when light enters a material depends on the wavelength of the lightVariation of Index of Refraction with Wavelength•The index of refraction for a material usually decreases with increasing wavelength•Violet light refracts more than red light when passing from air into a materialn=o/Refraction in a Prism•The amount the ray is bent away from its original direction is called the angle of deviation, δ•Since all the colors have different angles of deviation, they will spread out into a spectrum–Violet deviates the most–Red deviates the leastPrism Spectrometer•A prism spectrometer uses a prism to cause the wavelengths to separate•The instrument is commonly used to study wavelengths emitted by a light sourceUsing Spectra to Identify Gases•All hot, low pressure gases emit their own characteristic spectra•The particular wavelengths emitted by a gas serve as “fingerprints” of that gas•Some uses of spectral analysis–Identification of molecules–Identification of elements in distant stars–Identification of mineralsTotal Internal Reflection•Total internal reflection can occur when light attempts to move from a medium with a high index of refraction to one with a lower index of refraction–Ray 5 shows internal reflectionCritical Angle•A particular angle of incidence will result in an angle of refraction of 90°–This angle of incidence is called the critical angle2112nnfornnsin Chapter 23 Light :Geometric OpticsThin LensesThe Lens EquationProblem Solving for LensesA converging lensmay be thought of as a development of two prisms placed base to base. FA converging lensbrings parallel rays to a real focal point.The distance of the focal point from the center of the lens is called the focal length, f A diverging lens spreads out parallel rays as though they came from a virtualfocal pointf= +f= -QUICK QUIZ 23.4A plastic sandwich bag filled with water can act as a crude converging lens in air. If the bag is filled with air and placed under water, is the effective lens (a) converging or (b) diverging?QUICK QUIZ 23.4 ANSWER(b). In this case, the index of refraction of the lens material is less than that of the surrounding medium. Under these conditions, a biconvex lens will be divergent.The Lens Equation1/do+1/di=1/fF’ FO2F’dodifhohiImage Example Between F’ and OF’ FOBehind lens, virtual, uprightlarger than objectMagnifying glassF’ FOAt F’No imageLighthouseBetween F’ and 2F’F’ FO2F’Beyond 2F, real, inverted, larger ProjectorF’ FO2F’At 2F, real, inverted, same as object Office copierAt 2F’F’ FO2F’Between F and 2F,Real, inverted, smaller CameraBeyond 2F’F’O2F’At F, real, inverted,smallerFCameraAt infinityQUICK QUIZ 23.6An object is placed to the left of a converging lens. Which of the following statements are true and which are false? (a) The image is always to the right of the lens. (b) The image can be upright or inverted. (c) The image is always smaller or the same size as the object. Justify your answers with ray diagrams.QUICK QUIZ 23.6 ANSWER(a) False. A virtual image is formed on the left side of the lens if do < f. (b) True. An upright, virtual image is formed when do < f, while an inverted, real image is formed when do > f. (c) False. A magnified, real image is formed if 2f > do > f, and a magnified, virtual image is formed if do > f.Question: An object infinitely far from a converging lens has an image that is (a) real(b) virtual (c) upright(d) larger than the objectAnswer: aQuestion: An object farther from a converging lens than its focal point always has an image that is (a) inverted (b) virtual(c) the same in size(d) smaller in sizeAnswer: aQuestion: An object closer to a converging lens than its focal point always has an image that is(a) inverted (b) virtual (c) the same in size(d) smaller in sizeAnswer: bQuestion: The image of a real object formed by a