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Curved Refracting Surfaces: Lenses & Lens Aberrations

This lecture covers the topics of curved refracting surfaces, lenses, lens aberrations, thin lens equation, corrective optics, and an introduction to Kimberly Strong and electromagnetism. Reading assignments and upcoming quizzes are also mentioned.

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Curved Refracting Surfaces: Lenses & Lens Aberrations

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  1. PHY138 – Last Waves LectureToday’s overview • Curved Refracting Surfaces: Lenses • Lens Aberrations • Thin Lens Equation • Corrective Optics • Introduction to Kimberly Strong and Electromagnetism Quarter

  2. Reading Assignment Today’s reading assignment from the text by Knight was: Chapter 23, Sections 23.7 and 23.8 (This material is part of the course, and may appear on the final exam in April) Suggested Chapter 23 Exercises and Problems for Practice: 31, 73, 81

  3. Reading Assignment for January, 2006 Between now and January 9, please read Chapter 25, “Electric Charges and Forces”, Sections 25.1-25.6. There will be a masteringphysics Pre-Class quiz on Chapter 25 material, due Mon. Jan 9 by 10:00 AM.

  4. Lenses • Formed by two curved boundaries between transparent media. • Lenses may have spherical surfaces (lens-maker’s equation). Most modern lenses have non-spherical curved surfaces to avoid spherical aberration. • Every lens has a diameter, D, and focal length, f. • The ratio of (f / D) is called “f-number”. For example, an “f/6” lens has a focal length of 6 times its diameter.

  5. Diverging rays through a Converging Lens Focal length, f This follows from the principle of reversibility.

  6. Quiz 1 f • What will happen to the rays emerging to the right of the lens if the face is moved a little closer to the lens? • They will remain parallel. • They will diverge (spread out). • They will converge (toward a focus).

  7. Quiz 2 f • What will happen to the rays emerging to the right of the lens if the face is moved a little further away from the lens? • They will remain parallel. • They will diverge (spread out). • They will converge (toward a focus).

  8. Diverging rays through a Converging Lens Focal length, f s’ s

  9. Thin Lens Equation: sign conventions image object f s’ s s is positive for objects to the left of lens, negative for objects to the right of lens (virtual objects). s’ is positive for images to the right of lens, negative for images to the left of lens (virtual images). f is positive for converging lenses, negative for diverging lenses.

  10. The human eye • A near spheroid, about 22 mm from cornea to retina. • Focal length is 17 mm in relaxed state (distant vision) • Focal length is 14 mm in tensed state (near vision) • “Near Point” is about 25 cm for a normal eye. • “Far Point” is infinity for a normal eye.

  11. Corrective Optics 1 • Myopia is when the far point is less than infinity. (“near-sighted”) • The Myopic “near point” is usually closer than 25 cm. • A diverging lens moves the far point out to infinity, allowing for a crisp focus of distant objects.

  12. Corrective Optics 2 • Hyperopia is when the near point is signficantly greater than 25 cm. (“far-sightedness”) • The relaxed hyperoptic eye does not focus at infinity. By tensing the eye, distant objects can be seen. • A converging lens moves the near point closer and allows distant objects to be seen with a relaxed eye. • Many people develop hyperopia in their 40s or 50s.

  13. “Men and women are not content to comfort themselves with tales of gods and giants, or to confine their thoughts to the daily affairs of life; they also build telescopes and satellites and accelerators, and sit at desks for endless hours working out the meaning of the data they gather.” … Steven Weinberg (Nobel Prize in Physics 1979)

  14. PHY138 – ElectromagnetismLecture 0 • New instructor: Prof. Kimberly Strong • Room: MP710A • Email: strong@atmosp.physics.utoronto.ca • 6 weeks: January 9 to February 17, 2006

  15. In-Class Quiz When I grow up, I want to be: 1. A doctor 2. A physicist 3. A scientist (but NOT a physicist) 4. None of the above 5. I don’t know

  16. In-Class Quiz When I grow up, I want to be: 1. A doctor 2. A physicist 3. A scientist (but NOT a physicist) 4. None of the above 5. I don’t know 6. Any of the above!

  17. Syllabus for Q3 - Electromagnetism(parts of) Chapters 25 to 33 • Electric Forces and Electric Fields • Electric Potential Energy • The Electric Potential • Equipotentials and Energy in Capacitors • Currents, Resistance, and Resistivity • Circuits and Kirchoff’s Laws • Magnetic Fields and Magnetic Force • Electromagnetic Inductors

  18. Dates to Remember for the First Week of Q3 ... • The first week’s reading assignment is Chapter 25 of Knight, Sections 25.1 to 25.6 • 10:00 AM, Monday, January 9:Finish the first Mastering Physics pre-class quiz on this reading assignment • 11 AM, Monday, January 9: Our first lecture of 2006 here in Con. Hall • 11:59 PM on Friday, January 13:Finish the first MP problem set

  19. Have a great break! (and read Chapter 25) See you on January 9

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