Physics
Chapter 23: 1-5
Web Lecture
Optics: Reflection and Mirrors, Refraction and Lenses
Introduction
Let it be hypothesized that
straight lines are drawn out from the eye travel a distance of large magnitudes,
and that the figure enclosed by the sight-lines is a cone having its vertex at the eye and its base at the limits of the things seen,
and that these are seen where the sight-lines fall, and are not seen where the sight-lines do not fall,
and that things seen by a larger angle appear larger, while things seen by a smaller angle appear smaller,
and things seen by equal angles seem equal,
and that things seen by higher rays appear higher, while things seen by lower appear lower,
and similarly that things seen by rays more to the right appear more to the right, while those that appear by rays more to the left appear more to the left, and those by more angles appear more precise.
— Euclid, Optics
We use a ray model of light to discuss how light travels from a source to our eyes and how it can be reflected by mirrors and refracted by lenses. Later on, we will refine this model to explain the wave properties of light.
Web Lecture (Under Revision)
Since hands-on activities are most helpful in understanding light ray behavior, you can and should play with lenses.
The Physics Classroom site offers both discussion of optics phenomena, practical demonstrations, and interactive simulations. Use the (Reflection and the Ray Model of Light to review concepts covered in your text. If you are having problems with a particular concept, start with that concept and make sure that you understand it, then visit the other pages.
Practice with the Concepts
Complete the Check your Understanding questions in each section you review.
Discussion Points
- What is the focal length of a plane mirror? What is the magnification of a plane mirror?
- Although a plane mirror appears to reverse left and right, it doesn’t reverse up and down. Discuss why this happens, noting that front to back is also reversed. Also discuss what happens if, while standing, you look up vertically at a horizontal mirror on the ceiling.
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