1. Chapter 26 Review (and more test info)

2. Approved Equations The definition of index of refraction, Snell’s Law, and the lens and mirror equations

3. Unapproved Equations sin  = n 2 /n 1 isn’t an approved starting equation. Start with Snell’s Law, as that is more general. Then, if you’re doing a TIR problem, substitute the appropriate angle. Wavelength in a medium: n = vacuum /n

4. Bring to the test Hand calculator Scratch paper (optional)

5. During the test A paper ruler is printed on the equation page of the test. YOU MUST USE the paper ruler for the test problems in order to ensure that the scale I use for checking is the same on that you use for measuring. DO NOT USE your own centimeter ruler.

6. Skills/Knowledge for Ch. 26 See Ch. Reviews in the main menu of the course home page. Click on Chapter Objectives. See individual assignments for applications.

7. A Note about Ray Tracing Ray tracing problems tend to be emphasized on the AP exam. Therefore, I expect you to demonstrate ray-tracing techniques on the test. Be able to trace all the principle rays for mirrors and lenses, convex and concave. Know how to deal with real and virtual rays and be able to identify which is which. On your ray tracings, I expect you to differentiate virtual rays with dashed lines. In addition to curved mirrors and lenses, be able to trace rays for plane mirrors and for transparent prisms, such as rectangular and triangular solids. See the practice problems given in the R&R section of the schedule page.

8. More about Ray Tracing For curved mirrors and lenses, the primary skill is knowing how to trace the three principle rays. For plane mirrors, the key principle is the Law of Reflection and the fact that to locate an image, the reflected ray is traced backward behind the mirror. Two such rays from an object point are required to locate the corresponding image point. This is covered completely in P213. For rectangular and triangular prisms, ray tracing involves refraction across a boundary. Always draw a normal to the boundary first. Then use the fact that the ray bends toward the normal when entering a medium of greater index of refraction. If there’s more than one boundary, take them one at a time.

9. Two methods to solve curved lens/mirror problems Ray tracing affords an approximate way to locate an image of an object. The thin-lens equation (and corresponding mirror equation) allow you to calculate image positions. Expect to demonstrate the use of both of the above techniques. In addition… – The magnification equation allows you to calculate the image size relative to object size. – Be able to determine whether an image is real or virtual. – One other equation that may be helpful: f = R/2. (Focal length is half the radius of curvature.)

10. Some other things from Ch. 26 How a rainbow is formed (results from a combination of refraction and internal reflection) Dispersion by a prism: The speed of light in the medium is slightly dependent on the frequency of the light.