Exam 3 will be held in class on Friday, July 24. The exam will start promptly at 9:30 a.m. The exam will consist of 15 multiple-choice questions covering the material in the following chapters of Bueche and Wallach:  § Chapter 25, Section 2, plus Topic 1 below  § Chapter 26, Sections 1-7 and 9-12, plus Topic 2 below  § Chapter 27, Sections 1-4 and 13, plus Topic 3 below There will be at most two questions on Chapter 25. The remaining questions will be split roughly equally between reflection/mirrors and refraction/lenses. You are allowed to bring into the exam only the following:  § one formula sheet for Chs. 25-27 (letter-sized, no problem solutions)  § your formula sheets from Exams 1 and 2 (same restrictions as above)  § an electronic calculator  § pencils (number 2) and erasers The following topics, which are not covered in the textbook, may appear on the exam: Finite velocity of EM waves: Since an EM wave travels at a velocity v (where v=c in a vacuum), then in time t the wave travels a distance d=vt. Apparent depth: Suppose that an observer located in medium 2 sees light coming from an object located in medium 1 at a distance d beyond the interface between the two media. Then to the observer it appears that the object is located at an apparent distance from the interface d'=d mu(2) / mu(1), where mu(n) is the refractive index of medium n. Example: When an object 1.5 m beneath the surface of water [mu(1)=1.33] is viewed in air [mu(2)=1.00], the apparent depth of the object is d' = (1.5 m) (1.00) / (1.33) = 1.13 m. Two lenses in combination: You may be asked to find the image location, size, and type (real/virtual, upright/inverted) for any pair of thin lenses - not just for the case of virtual objects discussed in Section 27.13. The methods described in Section 27.13 can be used to solve the more general problems.