G1 THE NATURE OF EM WAVES AND LIGHT SOURCES G2 OPTICAL INSTRUMENTS HW/Study Packet Required: READ Tsokos, pp 598-620 SL/HL Supplemental: Hamper, pp 411-450 DO Questions p 605 #1,3 pp 621-623 #6,8,15,18,19,24,26 REMEMBER TO. Work through all of the example problems in the texts as you are reading them Refer to the IB Physics Guide for details on what you need to know about this topic Refer to the Study Guides for suggested exercises to do each night First try to do these problems using only what is provided to you from the IB Data Booklet Refer to the solutions/key ONLY after you have attempted the problems to the best of your ability UNIT OUTLINE I. THE NATURE OF EM WAVES AND LIGHT SOURCES A. ELECTROMAGNETIC WAVES AND THE SPECTRUM B. PROPERTIES OF LIGHT C. LASERS II. OPTICAL INSTRUMENTS A. LENSES AND RAY DIAGRAMS B. REAL AND VIRTUAL IMAGES C. MAGNIFYING GLASSES D. MICROSCOPES E. TELESCOPES F. LENS ABERRATIONS FROM THE IB DATA BOOKLET WHAT YOU SHOULD BE ABLE TO DO AT THE END OF THIS TOPIC Describe the nature of an electromagnetic wave and how it is produced Name the principle regions of the EM spectrum and sources of each State the meaning of the term dispersion and calculate the speed of light from indices of refraction Describe what a laser is, how it is created, and how it is used Find images of objects placed in front of lenses using graphical methods (ray diagrams) Find images of objects using algebraic methods Distinguish between real and virtual images and derive an expression for angular magnification Understand how compound microscopes and refracting telescopes work and calculate magnifications for each Explain spherical and chromatic aberrations and how to reduce them 1
HOMEWORK PROBLEMS: 1. In Galileo s attempts to measure the speed of light, a lantern was uncovered at a predetermined time and an observer some distance away was supposed to record the time that he first saw the lantern s light. a) If the lanterns were 8 km apart in this experiment, how long would it take light to travel this distance? [30 μs] b) Compare your answer in (a) to the typical reaction time for a human of about 0.2 s. 2. The diagram is a representation of the electromagnetic spectrum. In the diagram the region of visible light has been indicated. Indicate on the diagram above the approximate position occupied by a) infrared waves (label this I); b) microwaves (label this M); c) gamma rays (label this G). d) Outline the electromagnetic nature of light. visible light increasing frequency 3. The scattering of sunlight in the Earth s atmosphere accounts for the blue color of the sky. a) State approximate wavelengths for red light and blue light. b) With reference to your answers in (a), explain why the setting Sun appears reddish in color. 4. Laser light is an acronym for Light Amplification by the Stimulated Emission of Radiation and was invented in the 1960s. a) State two differences between the light emitted by a laser and that emitted by a filament lamp. b) The production of laser light relies on population inversion. Outline the meaning of the term population inversion. 2
c) Two overlapping beams of light from two flashlights (torches) fall on a screen. Explain why no interference pattern is observed. d) Outline how a laser can be used to read a bar-code. 5. The diagram (not to scale) shows three of the energy levels of a substance used to produce laser light. The energy of the ground state is E0. a) Draw an arrow on the diagram to indicate the transition that results in a population inversion. Label the arrow P. b) Draw an arrow on the diagram to indicate the transition that results in a pulse of laser light. Label the arrow L. c) Deduce that the wavelength of the emitted laser light is 690 nm. 6. The diagram, drawn to scale, shows a small object O placed in front of a thin convex (converging) lens. The focal points of the lens are shown, labelled F. The lens is represented by the straight line XY. a) On the diagram above, construct the paths of two rays in order to locate the position of the image formed by the lens. Label the image I. 3
b) Explain whether the image is real or virtual. [virtual] A converging lens, of focal length 5.0 cm, is used as a simple magnifying glass to view an object of length 0.80 cm. The observer s eye is very close to the lens. The image is formed at the near point (25 cm). c) Determine the distance of the object from the lens. [4.2 cm] d) Determine the length of the image. [4.8 cm] 7. A particular lens has a focal length of 9.0 cm and the image is formed at the near point which is 25 cm from the lens. Assuming that the eye is very close to the lens determine the a) distance of the object from the lens. [6.6 cm] b) angular magnification of the lens. [3.8] c) The angular magnification of the lens increases with decreasing focal length. State one disadvantage of using very short focal length lenses. [increased abberations] 4
8. This question is about a compound microscope, spherical aberration and chromatic aberration. a) An object O is placed in front of the objective lens of a compound microscope as shown below. The focal points of the objective lens are at F. The microscope is in normal adjustment. Without drawing a ray diagram, label the approximate positions, on the principal axis, of (i) the image produced by the objective lens (label this position X). (ii) the focal points of the eye lens (label these points E). (iii) the final image (label this image Y). b) An object is viewed through a convex lens that has been corrected for spherical aberration. For a particular object distance, the image of the object is as shown below. Another convex lens of the same focal length, but not corrected for spherical aberration, is now used to view the object. The object distance is unchanged. In the space below, draw the image as it would be seen through this second lens. The image as seen through the corrected lens is shown as a broken line. 5
9. The diagram below shows two rays of light from a distant star incident on the objective of an astronomical telescope. The paths of the rays are also shown after they pass through the objective lens and are incident on the eyepiece lens of the telescope. a) The principal focus of the objective lens is F O. On the diagram above, mark the position of the (i) principal focus of the eyepiece lens (label this F E ). (ii) image of the star formed by the objective lens (label this I). b) State where the final image is formed when the telescope is in normal adjustment. [at infinity] c) Complete the diagram in (a) to show the direction in which the final image of the star is formed for the telescope in normal adjustment. The eye ring of an astronomical telescope is a device that is placed outside the eyepiece lens of the telescope at the position where the image of the objective lens is formed by the eyepiece lens. The diameter of the eye ring is the same as the diameter of the image of the objective lens. This ensures that all the light passing through the telescope passes through the eye ring. d) A particular astronomical telescope has an objective lens of focal length 98.0 cm and an eyepiece lens of focal length 2.00 cm (ie f O = 98.0 cm, f E = 2.00 cm). Determine the position of the eye ring. [2.04 cm between eyepiece lens and the eye] 6