Physics 1252 Section Exam #1D

Transcription

1 Thu, 01 February 2018 Name: Physics 1252 Section Exam #1D Instructions: This is a closed-book, closed-notes exam. You are allowed to use a clean print-out of your formula sheet, any scientific calculator, and a ruler. Do not write on your formula sheet There is space after each question to show your work; if you need more space, you may use the back of the page, or request more paper. Please clearly indicate where your work for each problem is. Underline or draw a box around your final answer. The exam consists of four sections. Read all the questions at the start so that you can allocate your time wisely. Do easy ones first! You may not share your calculator. The use of cell phones or any other electronic devices (besides calculators) is prohibited. All such gadgets must be turned off and put away throughout the exam. Do not open the exam until told to begin. You have one entire class period (75 minutes) to finish the exam. Put your last name on every page of the exam. You must provide explanations and/or show work legibly to receive full credit for Sections III, IV and V. Make sure that your answers include appropriate units. Make sure you carry enough significant digits to get accurate results. By signing below, you indicate that you understand the instructions for this exam and agree to abide by them. You also certify that you will personally uphold the university s standards of academic honesty for this exam, and will not tolerate any violations of these standards by others. Unsigned exams will not be graded. Signature: UGACard #: Copyright c 2018 University of Georgia. Unauthorized duplication or distribution prohibited.

2 Section I II III IV V (Bonus) Score /20 (Skip) /40 /40 /10 I: Multiple-Choice Questions (20 points) For each question below, choose the single best response and write the corresponding capital letter in the box provided. There is no penalty for guessing the wrong answer. 1. A thin lens and a curved mirror both have the same focal length when surrounded by air (with index of refraction n Air = 1). If the lens and the mirror are submerged in water (with index of refraction n Water > 1) what happens to the focal length f L of the lens and the focal length f M of the mirror? A. f L decreases and f M decreases; B. f L stays the same and f M stays the same. C. f L changes and f M stays the same; D. f L stays the same and f M changes; E. f L increases and f M increases; 2. A light beam has a frequency of 480 THz in a material of refractive index 2.0. When the beam passes into another material with an index of refraction of 1.5, its frequency will be A. 480 THz. B. 360 THz. C. 240 THz. D. 640 THz. E. 320 THz. 3. Which of the following statements best explains why a telescope enables you to see the details of the Moon more clearly? A. The final image formed by the telescope is virtual rather than real. B. The final image formed by the telescope is closer to your eye than the original object is. C. The final image formed by the telescope is brighter than the original object is. D. The final image formed by the telescope has a larger angular size, subtended at the eye, than the original object. E. The final image formed by the telescope is inverted rather than erect, relative to the original object. Copyright c 2018 University of Georgia. 2

3 4. UGA waves weren t covered in class, but they do obey Snell s law! They have a speed of wave propagation v A = 2097m/s in apple juice and v B = 522m/s in butter milk. Also, assume that arcsin(522/2097) = o. A narrow beam of UGA waves striking a flat horizontal interface between apple juice and butter milk, with the apple juice above and the butter milk below the interface, will... A. always have an angle of refraction not exceeding o if the beam is incident from below the interface. B. undergo total internal reflection if incident from below the interface with an angle of incidence of 8.5 o. C. have an angle of refraction greater than the angle of incidence if the beam is incident from below the interface without total internal reflection. D. not undergo total internal reflection if incident from below the interface with an angle of incidence of 29.0 o. E. undergo total internal reflection if incident from above the interface with an angle of incidence of 29.0 o. Copyright c 2018 University of Georgia. 3

4 Worksheet I Copyright c 2018 University of Georgia. 4

5 Physics 1252 Section Exam #1A Physics Thu, 1252 Section 01 February Exam #1D Name: III: Refraction and Reflection at a Prism (40 points) III: Refraction and Reflection at a Prism (40 points) Surface T A 1 φ α α Glass n G 2 Surface L Surface R 3 B C γ The prism above has an isosceles triangular cross-section with base angle α = 50 o. Its top surface TThe is struck prismfrom above thehas outside an isosceles at pointtriangular A by incident cross-section light ray 1. with Thebase angle angle enclosed α = 55 o. Its top betweensurface ray 1 and T surface struckt from is φ = the 65 o outside. The prism at point is made A byout incident of glass, light withray an1. index Theofangle enclosed refraction between n ray 1 and surface T is φ = 75 o G = 1.60, and immersed in air with index. The of refraction prism isnmade A = out of glass, with an index o Only a few refraction reflected n G rays = 1.80, inside and the immersed prism, and in no air refracted with index rays of emerging refraction from n A the = prism 1.0. (if any?), Only are shown. a few reflected Recall that rays theinside sum ofthe interior prism, angles and inoany refracted trianglerays is 180 emerging o. from the prism (if any?), are shown. Recall that the sum of interior angles in any triangle is 180 o. (a) Find the angle of incidence and the angle of refraction at point A on surface T. (a) Find the angle of incidence and the angle of refraction at point A on surface T. (b) Is there a refracted ray emerging from the prism at point B on surface R? If so: at what angle of refraction? If not: why not? (b) Is there a refracted ray emerging from the prism at point B on surface R? If so: at what angle of refraction? If not: why not? (c) Is there a refracted ray emerging from the prism at point C on surface L? If so: at what angle of refraction? If not: why not? (c) Is there a refracted ray emerging from the prism at point C on surface L? If so: at what angle of refraction? If not: why not? Copyright c 2018 University of Georgia. 5

6 Worksheet III Copyright c 2018 University of Georgia. 6

7 IV: Image Formation in a Microscope (40 points) In a microscope, an objective lens (Lens 1) of +1.15cm focal length is placed to the right of an eyepiece lens (Lens 2) of +1.30cm focal length. Your eye is located very close to, and to the left, of the eyepiece. A bacterial cell is placed as the original object 1.20cm to the right of the objective lens. The final image produced by the eyepiece appears 20cm to the right of the eyepiece. Make a big, careful drawing of all this before you start!! (a) How far from the objective lens and to which side of it is the image produced by the objective lens? Is this image real or virtual? Is it erect or inverted relative to the original object. (b) Is the final image produced by the eyepiece real or virtual and, therefore, what is its image distance relative to the eyepiece? How far from the eyepiece is the eyepiece s object (=object from which the final image is produced)? How far apart are the two lenses? [Hint: The objective lens image found in (a) serves as the object to the eyepiece lens.] (c) If the original bacterial cell object is 11.0 µm in diameter what is the diameter of its final image, as seen through the eyepiece of the microscope? Is this final image erect or inverted relative to the original object? Copyright c 2018 University of Georgia. 7

8 Worksheet IV Copyright c 2018 University of Georgia. 8

9 3. Predict the location of the image of a candle flame placed 14 cm in front of a conca that has a focal length of 21 cm. What is the image magnification? What type of im V: A Mirror it? Calculate Image the answer and finish the drawing. (10 extra points bonus) Predict and draw the location of the image of a candle flame placed 18 cm to the left of a concave mirror that has a focal length of +27 cm, as follows: (a) How far from the mirror and on which side of it is the image located? What is the image s lateral magnification? What type of image is it: Real or Virtual? Erect or Inverted? Calculate the answers. (b) Draw the ray diagram for the formation of this image on the attached Worksheet. Make it large: at least half a page! Make it neat: use a ruler! Copyright c 2018 University of Georgia. 9

10 Worksheet V Copyright c 2018 University of Georgia. 10