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PHYS 221 Recitation

PHYS 221 Recitation. Kevin Ralphs Week 10. Overview. Multiple Lenses/Mirrors General Method Contact Lenses and Eye Glasses Refractive Power Angular Magnification -number. Multiple Lenses/Mirrors. General Method

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PHYS 221 Recitation

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  1. PHYS 221 Recitation Kevin Ralphs Week 10

  2. Overview • Multiple Lenses/Mirrors • General Method • Contact Lenses and Eye Glasses • Refractive Power • Angular Magnification • -number

  3. Multiple Lenses/Mirrors • General Method • Draw a picture showing the object of interest and the lenses/mirrors in the problem • Use the rules for ray tracing along with the thin-lens/mirror equation from Chapter 24 to find the location and magnification of the image produced by the first lens/mirror in the system • The image produced by the first lens/mirror then acts as the object for the second lens/mirror in the system. • Use ray tracing and the thin-lens/mirror equation a second time to find the image produced by the second lens/mirror in the system. Adapted from Giordano Textbook pg 910

  4. Multiple Lenses/Mirrors • Contact Lenses and Eye Glasses • A properly formed eye has a near point distance (the closest an object can be whilst in focus) equal to the 10 x the diameter of the eye, approximately 25 cm • Far-Sighted • This occurs when the near point distance is farther from the eye than normal • The corrective lens must then place near objects beyond the near point distance • Near-Sighted • This occurs when the near point distance is much closer • The corrective lens must then take far-away objects (those out at infinity) and place them within their ability to focus • The difference between glasses and contact lenses is that eye glasses have a distance between the two lenses

  5. Refractive Power • What does it tell me? • Refractive power gives an idea as to how strong the corrective power of a lens is refractive power • Measured in diopters: • Why should I care? • This makes explicit the relationship between the strength of a lens and the focal distance

  6. Angular Magnification • What does it tell me? • The enlargement of an image on the retina • Why should I care? • Before when we spoke of magnification, it was linear magnification which requires knowledge of distances • Distances are not always directly measurable (think of the stars) so angles are more useful

  7. Angular Magnification : Near point distance : Focal Distance of the objective lens : Focal distance of the eyepiece : Focal distance of the mirror

  8. - number • What does it tell me? • How dark an image is projected through a camera lens system -number • Why should I care? • The exposure of film needs to be within a certain range • However, for fast motion a fast shutter speed is necessary to keep the image from blurring • Adjusting the -number compensates for this

  9. Quiz Problem #1 A person’s near-point distance is about 40 cm. What is the focal length of this person’s glasses if using them allows them to bring a newspaper to within 10 cm of his eye? Assume the glasses are placed 2.0 cm in front of his eyes. • 6.67 m • 7.92 m • 15.4 m • 14.6 m

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