Unit II On-a-Page


Instructor’s Note


This Unit is very heavy on vocabulary, there is a set on flashcards on Quizlet to help you.

  • An is a lens or mirror.
  • An is the apparent reproduction of an object, formed by an optical element (or collection of them) reflecting and/or refracting light.
  • Images can either be (same orientation as object) or (upside-down with respect to object).
  • The optical axis is a line that passes through the optical element perpendicular to it
  • The point where the optical axis meets the optical element is called the .
  • The of a lens is where the lens is thickest (for a converging lens) or thinnest (for a diverging lens).
  • The of a mirror is the center of curvature.
  • Image i and object  o distances are measured along the optical axis.
  • Signs are relative to the path of the light.
  • If the object is on the same side as the incoming light, then  o > 0 , otherwise  o < 0 .
  • If the image is on the same side as the outgoing light, then  i > 0 , otherwise  i < 0 .
  • For a lens, the incoming and outgoing sides are different (light goes through a lens).
  • For a mirror, the incoming and outgoing sides are the same (light bounces off a mirror).
  • Focal lengths are also signed. If the element tends to incoming parallel light (a or a ), then the focal length is negative. If the element incoming parallel light ( or ), the focal length is positive.

Principles for Unit II

This unit in particular has a lot of terminology. To help you stay focused, the principles (where we will begin analyzing situations) are:
How light interacts with surfaces and materials
  • Law of reflection which is best understood in the particle picture.
  • Law of refraction which is best understood in the wave picture.
  • Light slows when it enters a medium, but the energy of a photon cannot change. So the wavelength must!
Optical elements and ray diagrams
  • The position of the image formed by an optical system is located at  \frac{1}{i} + \frac{1}{o} = \frac{1}{f} where:
    •  o is the object distance, using the sign conventions used above.
    •  i is the image distance, using the sign conventions used above.
    •  f is the focal length with its correct sign.
  • For ray diagrams: one ray in parallel and out through focal point, one ray in through focal point and out parallel, one ray using the center of the system.
  • And point where photons seem to emerge can be used as an object. Such a point could be a real source of photons (an object) or an image from another optical element.


Icon for the Creative Commons Attribution 4.0 International License

Physics 132: What is an Electron? What is Light? by Roger Hinrichs, Paul Peter Urone, Paul Flowers, Edward J. Neth, William R. Robinson, Klaus Theopold, Richard Langley, Julianne Zedalis, John Eggebrecht, and E.F. Redish is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

Share This Book