Chapter 36Thin lensesConverging and diverging Lens ShapesFocal Length of a Converging LensFocal Length of a Diverging LensNotes on Focal Length and Focal Point of a Thin LensRay Diagrams for Thin Lenses – convergingThe 3-ray diagram againSlide 9Object distance, 5 cases: 1 -- 2Object distance, 5 cases: 3 -- 4Object distance, 5 cases: 5Ray Diagrams for Thin Lenses – DivergingSlide 14Slide 15The CameraThe EyeThe Eye – Close-up of the CorneaCombinations of Thin LensesCombination of Thin Lenses, exampleChapter 36Image Formation 21. Thin Lens2. Multi lens/mirror systemThin lensesLenses are commonly used to form images by refraction. We discuss about spherical lenses only. They are part of two spheres.There are two types of lensesConvergingDivergingWhen the thickness of the lens is negligible, the lens is called thin lens.Principal axis: the line that goes through the two centers of the two spheres.Paraxial rays are those close to the principal axis.Lenses are used in optical instrumentsCamerasTelescopesMicroscopesconvergingdivergingPrincipal axisPrincipal axisConverging and diverging Lens ShapesConverging:positive focal lengthsthickest in the middleDiverging:negative focal lengthsthickest at the edgesFocal Length of a Converging LensThe parallel rays pass through the lens and converge at the focal pointThe parallel rays can come from the left or right of the lensFocal Length of a Diverging LensThe parallel rays diverge after passing through the diverging lensThe focal point is the point where the rays appear to have originatedNotes on Focal Length and Focal Point of a Thin LensBecause light can travel in either direction through a lens, each lens has two focal pointsOne focal point is for light passing in one direction through the lens and one is for light traveling in the opposite directionHowever, there is only one focal lengthEach focal point is located the same distance from the lensRay Diagrams for Thin Lenses – converging Ray diagrams are convenient for locating the images formed by thin lenses or systems of lensesFor a converging lens, the following three rays are drawn:Ray 1 is drawn parallel to the principal axis and then passes through the focal point on the back side of the lensRay 2 is drawn through the center of the lens and continues in a straight lineRay 3 is drawn through the focal point on the front of the lens (or as if coming from the focal point if p < ƒ) and emerges from the lens parallel to the principal axisThe image is realThe image is invertedThe image is on the back side of the lensPLAYACTIVE FIGUREThe 3-ray diagram againRay 1:Parallel to axis, then passes through far focal point Ray 2:Passes unchanged through center of lens Ray 3:Passes through near focal point, then parallel to axisFFfObjecthodoReal image, inverted, smallerhidioioiddhhm :ionmagnificatObject distance, 5 cases: 1 -- 2FFf2fReal, inverted, smallerFFf2fReal, inverted, same sizeFFf2fReal, inverted, largerFFf2fNo imageObject distance, 5 cases: 3 -- 4FFf2fVirtual, upright,largerLike in the converging mirror case, there are 5 possible object locations that produce different images.While in the diverging lens case, like in the diverging mirror case, no matter where the object is placed, you always get a virtual, upright and smaller image.Object distance, 5 cases: 5Ray Diagrams for Thin Lenses – Diverging For a diverging lens, the following three rays are drawn:Ray 1 is drawn parallel to the principal axis and emerges directed away from the focal point on the front side of the lensRay 2 is drawn through the center of the lens and continues in a straight lineRay 3 is drawn in the direction toward the focal point on the back side of the lens and emerges from the lens parallel to the principal axisThe image is virtualThe image is uprightThe image is smallerThe image is on the front side of the lensThe 3-ray diagram againRay 1Parallel to axis, virtual ray passes through near focal point Ray 2Straight through center of lens Ray 3Virtual ray through far focal point, virtual ray parallel to axisFFfObjecthodoVirtual image, upright, smallerhidiThe CameraThe photographic camera is a simple optical instrument ComponentsLight-tight chamberConverging lensProduces a real imageFilm behind the lensReceives the imageThe EyeThe normal eye focuses light and produces a sharp imageEssential parts of the eye:Cornea – light passes through this transparent structureAqueous Humor – clear liquid behind the corneaThe Eye – Close-up of the CorneaCombinations of Thin LensesThe image formed by the first lens is located as though the second lens were not presentThen a ray diagram is drawn for the second 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 systemCombination of Thin Lenses,
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