Physics 213 General PhysicsSlide 1Are the red and violet lights coming from the same raindrop?Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Funny MirrorSlide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Ray Diagram for Diverging LensA 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.Slide 29Slide 30Slide 31Slide 32Slide 33Sign Conventions for MirrorsSign Conventions for Refracting Surfaces/LenesCombinations of Thin LensesPhysics 213General PhysicsLecture 162Last Meeting: Reflection and Refraction of LightToday: Mirrors and Lensest3Are the red and violet lights coming from the same raindrop?Dispersion by drops of water. Red is bent the least so comes from droplets higher in the sky.5Why is the sky blue?Why is the sunset orange?hint6Why is the cloud white?7891011∞12demo131415Funny Mirror161718192021222324252627Ray Diagram for Diverging LensThe image is virtualThe image is uprightQUICK 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.Image 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 infinityExample: (a) An object 31.5 cm in front of a certain lens is imaged 8.20 cm in front of that lens (on the same side as the object). What type of lens is this and what is its focal length? Is the image real or virtual? (b) If the image were located, instead, 38.0 cm in front of the lens, what type of lens would it be and what focal length would it have? Solution: (a) 1/do+1/di=1/f where do=31.5 cm, di=-8.20 cm1/31.5+1/(-8.20)=1/f, which yields f=-11.1 cm, thusdiverging lens. The image is in front of the lens, so it is virtual(b) Similarly, we have 1/31.5+1/(-38.0)=1/f. which gives f=+184 cm, thus, converging lens. F’ FO(b)FImageF’(a)32Question: An object infinitely far from a converging lens has an image that is (a) real(b) virtual (c) upright(d) larger than the objectAnswer: a33Question: 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: a34Quiz: 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: bSign Conventions for Mirrors1 1 2p q R '1 1 1h qMh pp q f Concave gives “+” conventionsSign Conventions for Refracting Surfaces/LenesThese are the same sign conventions – so just remember them for thin lenses. 1 21 1 1( 1)nf R R 12'n qhMh n p n1 is the source mediumn2 is the observing mediumRnnqnpn1221'1 1 1h qMh pp q f Combinations of Thin LensesThe image produced by the first lens is calculated as though the second lens were not presentThe light then approaches the second lens as if it had come from the image of the first lensThe image of the first lens is treated as the object of the second lensThe image formed by the second lens is the final image of the systemIf the image formed by the first lens lies on the back side of the second lens, then the image is treated at a virtual object for the second lensp will be negativeThe overall magnification is the product of the magnification of the separate
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