Download Maximum Reflection of Red Light - Optics and Modern Physics - Past Paper and more Exams Physics in PDF only on Docsity! Physics 228 - First Common Hour Exam February 19, 2006 Prof. Coleman and Dr. Francis =⇒ Your name sticker with exam code =⇒ Your signature Turn off and put away cell phones now! 1. The exam will last from 3:00 PM to 4:20 PM. Use a #2 pencil to make entries on the answer sheet. Enter the following ID information now, before the exam starts. 2. In the section labeled NAME (Last, First, M.I.) enter your last name, then fill in the empty circle for a blank, then enter your first name, another blank, and finally your middle initial. 3. Under STUDENT # enter your 9-digit student ID. 4. Enter 227 under COURSE, and your section number (see label above) under SEC. 5. Under CODE enter the exam code given above. 6. During the exam, you may use pencils, a calculator, and one handwritten 8.5 x 11 inch sheet with formulas and notes, without attachments. 7. There are 15 multiple-choice questions on the exam. Mark only one answer on the answer sheet. There is no deduc- tion of points for an incorrect answer, so even if you can- not work out the answer to a question, you should make an educated guess. At the end of the exam, hand in the answer sheet and the cover page. Retain this question paper for future reference and study. 8. When you are asked to open the exam, make sure that your copy contains all 15 questions. Raise your hand if this is not the case, and a proctor will help you. Also raise your hand during the exam if you have a question. 9. Please SIGN the cover sheet under your name sticker and have your student ID ready to show to the proctor during the exam. Some possibly useful information: c = speed of light = 3.00 × 108 m/s me = electron mass = 9.11 × 10 −31 kg mp = proton mass = 1.67 × 10 −27 kg 1 mHz = 10−3 Hz 1 kHz = 10+3 Hz 1 MHz = 10+6 Hz 1 GHz = 10+9 Hz 1 nm = 10−9 m 1 Å = 10−10 m = 0.1 nm cos(α ± β) = cos(α) cos β ∓ sin(α) sin(β) sin(α ± β) = sin(α) cos(β) ± cos(α) sin(β) 1. The thinnest film of oil (n=1.50) floating on water (n=1.33) that would give maximum reflection of red light (λ0=680 nm) is a) 227 nm b) 113 nm c) 170 nm d) 256 nm e) 128 nm 2. A radio station operating at frequency 99.5 MHz broadcasts from two towers. What is the farthest distance the towers can be apart to make sure there are no “dead zones”, places where the radio signal is completely canceled out by destructive in- terference? a) 3.0 m b) 1500 km c) 0.17 m d) 0 m e) 1.5 m 3. An unpolarized beam of light is incident in air onto the surface of a flat glass slab (n = 1.5). The reflected light is completely plane polarized. What is the angle of refraction (θt) for the light transmitted into the glass? a) 90◦ b) 28.1◦ c) 45◦ d) 33.7◦ e) 21.7◦ θt θ1 4. A thin film of index n = 1.55 deposited on a glass slide (n = 1.50), as shown, is to be used as an optical waveguide. To op- erate properly, total internal reflection must occur at both the film-air and the film-glass interfaces. What is the maximum entrance angle θ that light ray can have for this to work? n = 1.00 n = 1.55 n = 1.50 θ a) 75◦ b) 23◦ c) 35◦ d) 47◦ e) 14.5◦ 5. A concave mirror has focal length f > 0. A real object is placed a distance 2f from the mirror. Then the image is a) Real; inverted; same size as object b) Real; inverted; smaller c) Virtual; upright; bigger d) Virtual; upright; smaller e) Real; inverted; bigger 6. An polarized beam of light is incident on a group of two polar- izing sheets that are lined up so that the polarizing axis of the first sheet is rotated by 30◦ with respect to the polarization of the incident light, and the polarizing axis of the second sheet is rotated by 30◦ with respect to the polarizing axis of the first sheet. What fraction of the incident intensity is transmitted? a) 9/16 b) 3/4 c) 27/64 d) 1/4 e) 2/3
