question 9 - PHYSICS 117B MID-TERM EXAMINATION 1 FEBRUARY 7...

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P HYSICS 117B — M ID -T ERM E XAMINATION 1 — F EBRUARY 7, 2005 The test relates to the material of chapters 20, 21, 22, 23, and 24 of Knight’s Physics for Scien- tists and Engineers . For the multiple-choice questions 1-15, choose what you believe to be the correct answer and mark that answer on the OPSCAN sheet. Three problems are presented on pages 5-6-7. Choose two of these three problems to solve and write the word "Omit" on the other one. Clearly show your work for possible partial credit. M ULTIPLE -C HOICE Q UESTIONS (4 POINTS EACH , TOTAL 60 POINTS ) 1. The image produced by a convex mirror of an erect object in front of the mirror is always a. virtual, erect, and larger than the object. b. virtual, erect, and smaller than the object. c. real, erect, and larger than the object. d. real, erect, and smaller than the object. e. none of the above. 2. Light passes from one medium in which the speed of light is v 1 into another in which the speed of light is v 2 , where v 1 < v 2 . As the light passes the boundary, a. neither f nor λ changes b. f increases, λ decreases. c. f does not change, λ increases. d. f does not change, λ decreases. e. f decreases, λ increases. The frequency is the same in both media. However, if v 1 < v 2 , the index of refraction in medium 1 is greater than that in medium 2. Hence the wavelength is shorter in medium 1, and it increases upon passing into medium 2. 3. An object is in front of a converging lens. The distance from the lens to the object is less than the focal length of the lens. The image is
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Physics 117B — Examination 1 — Chapters 20-24 — February 7, 2005 P AGE 2 OF 8 P AGES 4. You shine white light on a soap bubble that is filled with air and suspended in air. The thick- ness of the wall of the bubble is d and the index of refraction of the bubble's material is n . White light is projected onto the surface of the bubble at normal incidence. The frequency, f , of light that is strongly reflected from the bubble obeys the equation, where m is an integer. The correct answer is (b). Light from the front surface of the bubble experiences a phase shift of ! radians upon reflection, while light from the back surface of the bubble does not. This means that the condition for constructive interference on reflection is that the phase difference between the front and back-surface rays shall be a multiple of 2 ! : Δφ = 2 π 2 nd λ − π = 2 m π ⇒ 2 nd λ = 2 ndf c = m + 1 2 2 ndf = m + 1 2 c 5. A flat plate of transparent material S is in contact with a flat plate of transparent material T.
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