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NSCI 122: TEST STUDY QUESTIONS & TASKS

Part I. Physics Preliminaries

  1. Know how to write a number in scientific notation (Exercise 1).
  2. Know how to add, subtract, multiply, and divide numbers expressed in scientific notation (Exercise 1).
  3. Know how to convert a quantity from one set of units to another set of units using conversion factors (Exercise 2).
  4. Know the sequence of steps that comprise the “scientific method”, i.e. know how we do good science.
  5. What does a force do to an object?
  6. If work is done by a force on an object, what happens to the object?
  7. Describe what energy is. Energy is needed to do what?
  8. How fast work gets done (or how fast energy is supplied or used up) is a physical quantity that we call what?
  9. What are the mks units of force, work, energy, and power?
  10. The electric force is only exerted between objects with what fundamental physical property?
  11. How do we model an electron on the Sun exerting an electric force on an electron on your arm? What physical quantity do we introduce to explain this “action at a distance”?
  12. What are the two basic ways that light energy can be emitted?

Part II. Wave Preliminaries

  1. Describe an electromagnetic (light) wave. Draw a sketch of one.
  2. What is it that is ‘waving’ in a light wave?
  3. Describe what is meant by the wavelength and frequency of a light wave. What are the mks units of these two quantities?
  4. What is the speed of light in vacuum or air?
  5. How is the speed of a wave related to the wavelength and frequency?
  6. Know the order of the electromagnetic spectrum from low frequency (long wavelength) to high frequency (short wavelength). Know the order of the visible part of the spectrum from low frequency (long wavelength) to high frequency (short wavelength).
  7. Define the index of refraction (or refractive index) of a material.
  8. What happens to the speed of light when it enters a medium with a higher refractive index? a lower index? What happens to the wavelength of the light in each case? to the frequency of the light?

Part III. Geometric Optics

  1. What is a ray?
  2. What is meant by the ‘angle of incidence’?
  3. What does the Law of Reflection state?
  4. What does the Law of Refraction (Snell’s Law) state?
  5. As the angle of incidence increases from zero (normal incidence) and gets bigger, what happens to the amount of reflected light?
  6. What is the critical angle? What is total internal reflection (TIR)? Does TIR occur for incident angles bigger or smaller than the critical angle? Does the refractive index of the incident medium have to be smaller or larger than the refractive index of the reflecting medium for TIR to occur?
  7. Given two materials and the incident ray, draw the reflected and refracted ray. (Exercise 4)
  8. Describe the operation of an optical fiber. Why are optical fibers preferred over copper wires for sending information?
  9. What is dispersion of light?
  10. For materials with normal dispersion, does shorter wavelength light get bent more or less compared to longer wavelength light? So does blue light get bent more or less than red light?
  11. Where does your image appear to be when you look in a plane mirror? Is this a virtual or real image?
  12. Describe what is meant by a virtual image. Do the light rays converge or diverge as they enter your eye when viewing a virtual image?
  13. Describe how an image is formed above the object when the object is viewed through a block of glass or through a pool of water. Sketch the rays showing the formation of the image. Is this a virtual or real image?
  14. Is a positive (converging) lens thicker in the middle or thinner in the middle? If a beam of collimated light is sent through a positive lens, what happens to the light?
  15. Is a negative (diverging) lens thicker in the middle or thinner in the middle? If a beam of collimated light is sent through a negative lens, what happens to the light?
  16. What is meant by the focal point of a positive lens? of a negative lens?
  17. Describe a real image and a virtual image.
  18. Can a positive lens be used to form a real image, a virtual image, or both?
  19. Can a negative lens be used to form a real image, a virtual image, or both?
  20. Be able to perform a ray trace for either a single positive lens or a single negative lens. Be able to label the object distance (p), the image distance (q), the focal point (F), and the focal length (f ) on the ray trace.
  21. Does a simple camera use a positive or negative lens? Is the object close or far from the lens? Is the image real or virtual? Is the image formed on the same side of the lens as the object or on the other side? Is the image bigger than the object or smaller? Is the image right-side-up or upside down? Where do you put the film? Show a ray trace for a simple camera.
  22. Does a simple projector use a positive or negative lens? Is the object close or far from the lens? Is the image real or virtual? Is the image formed on the same side of the lens as the object or on the other side? Is the image bigger than the object or smaller? Is the image right-side-up or upside down? Where do you put the screen? Show a ray trace for a simple projector.
  23. Does a simple magnifying glass use a positive or negative lens? Is the object close or far from the lens? Is the image real or virtual? Is the image formed on the same side of the lens as the object or on the other side? Is the image bigger than the object or smaller? Is the image right-side-up or upside down? About how far should the image be from the lens so that it looks as large as possible without being blurry? Show a ray trace for a simple magnifying glass.
  24. Sketch the eye and label the following main parts: cornea, iris, pupil, lens, ciliary muscles, retina, optic nerve. Where do you want images to be formed in your eye?
  25. What are rods and cones? Which enable you to see colors? Which work best in bright light? Which work best in low light levels?
  26. How does your eye focus on objects at various distances?
  27. If you suffer from myopia (near-sightedness), what is basically wrong with the image formation of your eye? Will a negative or positive lens correct this? Why?
  28. If you suffer from hyperopia (far-sightedness), what is basically wrong with the image formation of your eye? Will a negative or positive lens correct this? Why?
  29. How do you find the lens power of a lens with a focal length of f ? What are the standard units of lens power?
  30. During the day, to what wavelength are our eyes most sensitive? What color of light is this? During the night, does the wavelength of peak sensitivity increase or decrease?
  31. Why does a red shirt appear red? What are the two basic optical phenomena that are occurring here?
  32. Is the absorption of light important in explaining the subtractive mixing or additive mixing of colors?
  33. What are the three primary colors for the subtractive mixing of colors? What colors do you get if you mix any two of the primary colors together? What color do you get if you mix all three primaries?
  34. What are the three primary colors for the additive mixing of colors? What colors do you get if you mix any two of the primary colors together? What color do you get if you mix all three primaries?
  35. What is meant by spherical aberration of a lens? What is a standard way to correct for it?
  36. What is meant by chromatic aberration of a lens? What is a standard way to correct for it in high quality optical systems?

Part IV. Physical Optics

  1. When two light waves meet, they interfere to form an interference pattern. There are points of perfect constructive interference and points of perfect destructive interference in the pattern. Is the light brightest at points of constructive or destructive interference? Are the points where there is no light points of constructive or destructive interference?
  2. If two waves leave the same place in phase (crest on crest), but then one travels a longer distance before they meet again, will they interfere constructively or destructively? Explain how the extra length traveled by the one wave determines this answer. For what values of this extra distance will the waves interfere perfectly constructively? For what values of this extra distance will they interfere perfectly destructively?
  3. Describe the interference pattern formed by monochromatic light going through two slits. Is there a bright spot or dark spot at the center of the pattern? Are the bright spots of equal width?
  4. What happens to the bright spot spacing of the double slit pattern if the slits get closer together? If the wavelength decreases?
  5. What is a diffraction grating in simple terms?
  6. Describe the interference pattern formed by monochromatic light going through a diffraction grating. In what ways is it similar to the pattern from two slits? In what ways is it different?
  7. What is the main application of a diffraction grating?
  8. Sketch a Michelson interferometer. Label the main components. Where do the two beams come from that interfere?
  9. What are some uses of an interferometer?
  10. Where do the two beams come from that interfere in thin film interference? Where does the light source have to be if you are to see the interference pattern?
  11. Why do you see different colors when you see the thin film interference from a soap bubble?
  12. Describe how a simple transmission hologram is made and how it is viewed.
  13. What is meant by the diffraction of light?
  14. What conditions are there on the size of the aperture or obstacle if you are to see observable diffraction effects?
  15. Describe the diffraction pattern formed by monochromatic light going through a single slit. Sketch a graph of the brightness of the light versus position on the screen. Where does most of the light go? How wide is the central diffraction peak compared to the other bright spots? What happens to the pattern if the slit is narrowed?
  16. Describe the diffraction pattern formed by monochromatic light going through a circular aperture. Where does most of the light go? What is “Airy’s disk”? What are “Airy’s rings”?
  17. What is “Poisson’s spot”? Why did its presence persuade a lot of people that light is a wave, rather than a stream of particles (corpuscles) as put forth by Newton?
  18. Why can you improve your television reception sometimes by standing at certain places in your room? This previous question is only for televisions that have antennas, not cable TVs. Why?
  19. What is meant by the polarization of a light wave?
  20. List and describe the various states of polarization.
  21. Light from room lights and direct sunlight is mostly in which polarization state?
  22. What is a dichroic polarizer? What is a common name for such a polarizer? If unpolarized light is sent through a dichroic polarizer, what happens to the outgoing light?
  23. What is meant by the polarization axis of a dichroic polarizer?
  24. If light is sent through two dichroic polarizers whose polarization axes are parallel, what happens to the outgoing light? If the polarization axes are crossed? If the polarization axes are not completely crossed?
  25. What is meant by the polarization angle or Brewster angle when unpolarized light reflects off a surface? Describe the direction of the electric field if light is linearly polarized upon reflection. As the angle of incidence gets farther away from the Brewster angle, what happens to the polarization of the reflected light?
  26. How does a polaroid film reduce glare? In which direction should the polarization axis of the film be to reduce glare?
  27. What is meant by a birefringent material? What is a common birefringent material?
  28. Describe the formation of the ordinary and extraordinary beams in a birefringent crystal. Describe the polarizations of the two beams.
  29. If linear polarized light is sent into a birefringent crystal, what can happen to the output light? What do these possibilities depend on?
  30. What is meant by an optically active material? What is a common optically active material?
  31. What does an optically active material do to linearly polarized light if it is sent through the material?
  32. Describe the process of "scattering". How is it different from reflection?
  33. What determines the type of scattering that will occur?
  34. For Rayleigh scattering, is the amount of scattered light dependent on the wavelength of the light? If so, in what way?
  35. Explain why the sky looks blue and the sun looks yellow when the sun is overhead. Explain why the sky looks red and the sun orange/red at dawn and dusk.
  36. Describe the process of "absorption". Where does the energy from the light go when it is absorbed?
  37. What is meant by an "absorption spectrum" for a material? What is the significance of a peak in such a spectrum?

Part V. Quantum Optics

  1. What is meant by thermal radiation?
  2. Sketch a typical power spectrum (power vs. wavelength) for an object's thermal radiation at two different temperatures of the object. Be sure to know the differences in the two spectra.
  3. If the temperature of an object increases, what happens to the peak wavelength of its thermal radiation? What happens to the total radiated power?
  4. What does the wave theory of light predict for the power spectrum of thermal radiation?
  5. Who successfully explained the observed power spectrum using the ideas of quantized radiation?
  6. What is a photon? How would you best describe one.
  7. Einstein stated that a photon can be viewed as a particle. What is the mass of the photon particle? Does it carry a momentum? How do you find the energy of a photon?
  8. Photon 1 has a higher frequency than Photon 2. Which photon carries more energy? Which has the shorter wavelength?
  9. Which carries more energy: a red photon or a blue photon?
  10. How does the energy of a typical photon compare to energies of ordinary, macroscopic objects? What is an approximate energy of a red photon?
  11. A laser is delivering a certain power in its beam. The output power in the beam then increases. What has happened to the number of photons emitted per second by the laser? What has happened to the energy of an individual photon?
  12. What is the photoelectric effect?
  13. Who successfully explained the photoelectric effect for the first time?
  14. What basic premise was made about the photons and electrons in explaining the photoelectric effect?
  15. What is meant by the wave-particle duality of light?
  16. Does the wave-particle duality also extend to objects or particles that are made out of matter? What proof do we have that particles made of matter can at times act as waves?
  17. Can an atom have any value of energy? Are the energies of an atom continuous or discrete?
  18. What do we mean when we say that “The energies of an atom are quantized.”?
  19. Are the emission spectra of excited atoms continuous or discrete?
  20. How do the ideas of quantized energy levels for an atom and the photon model of light explain the discrete emission spectra of excited gases? the discrete absorption spectra?
  21. What does the acronym laser stand for?
  22. Distinguish between spontaneous emission and stimulated emission of light in an excited atom. Which usually occurs first in an ordinary atom?
  23. Describe the operation of a three-level laser. What is meant by a population inversion? What is the role of the metastable level?
  24. What are the three necessary components to build a laser? Describe the role of each component in the operation of a laser.
  25. Can the gain medium of a laser be a solid? a liquid? a gas?
  26. What are usual excitation sources for solid lasers? for liquid lasers? for gas lasers?
  27. What is the difference between continuous wave operation and pulsed wave operation of a laser? Why would you want to operate a laser in continuous wave? Why would you want to operate a laser in pulsed wave?
  28. Describe the characteristics of a typical laser output beam.
  29. Be familiar with at least one kind of solid laser and one kind of gas laser. What kind of output light (IR, UV, color)? What type of excitation source? Typical application? Any other characteristics?
  30. Briefly describe the operation of a semiconductor laser. What are advantages of using semiconductor lasers versus conventional lasers? Any disadvantages?
  31. What are some applications of semiconductor lasers?

Part VI. Theory of Relativity

  1. What does it mean if two objects are in relative motion?
  2. Will two people in relative motion measure the same speed for an object that is moving relative to them?
  3. How fast does light travel in free space? Does this speed depend on how fast you are moving relative to the light source?
  4. Define a “proper time interval” and a “nonproper time interval”.
  5. What does the principle of “time dilation” state?
  6. Define a “proper length” and a “nonproper length”.
  7. What does the principle of “length contraction” state?
  8. Define the “rest mass” of a particle.
  9. Define the “rest energy” of a particle.
  10. Define the “relativistic mass” of a particle.
  11. Why can’t a particle with a nonzero rest mass travel at the speed of light? (You should be able to argue this by either discussing what happens to the mass and acceleration of a particle being accelerated by a constant force or by discussing the energy requirements needed to keep increasing the speed of a particle.)
  12. What is the rest mass of a photon?
  13. Does the theory of relativity predict that time travel is possible? If so, describe the exact kind of time-travel predicted.