Hobson Physics: Concepts & Connections 4e

CHAPTER 13 review questions The Post-Newtonian Revolution 1. What is quantum physics? 2. Describe at least one way in which the philosophical implications of quantum physics differ from those of Newtonian physics. The Quantization of Light and the Quantum World 3. Describe the double-slit experiment with light and its outcome. 4. What is an electromagnetic field? 5. If we perform the double-slit experiment with dim light and a short exposure time, what will we see on the screen? 6. Following up on the preceding question, what will we see after a longer exposure time? 7. What do we mean by a quantized electromagnetic field? 8. How big is the smallest allowed energy increment in a quantized EM field? 9. What do we mean by a quantum (or energy quantum) of the EM field? 10. What is a photon? What is its speed? Its rest-mass? 11. Why don’t we normally notice that light is made of photons? 12. How does quantum uncertainty enter into the double-slit experiment with light? 13. How does quantum nonlocality enter into the double-slit experiment with light? Electron Interference and the Quantum Mystery of Matter 14. Can a single electron have a wavelength? 15. How do we know that material particles are accompanied by waves? 16. What name do we give to the waves that accompany material particles? 17. Which detects the smallest objects: a visible light microscope or an electron microscope? Why? 18. Describe the double-slit experiment with electrons and its outcome. 19. If we perform the double-slit experiment with electrons using a low intensity beam and a short exposure time, what will be see on the screen? 20. Following up on the preceding question, what name do we give to the individual impacts? 21. What evidence is there that a field called a “matter field” exists? 22. What do we mean when we say that matter fields are quantized? Quantum Uncertainty 23. Describe an example in which identical causes do not result in identical outcomes. 24. How does quantum uncertainty differ from the ordinary uncertainty in the outcome of a coin flip? conceptual exercises The Post-Newtonian Revolution 1. Name the two revolutionary physics theories of the first decade of the twentieth century. 2. What are some practical ways in which quantum physics has impacted modern life? The Quantization of Light and the Quantum World 3. How do we know that light is quantized? 4. In what sense are EM fields “digital” rather than “analog”? 5. A photon impact appears on the screen in the double-slit experiment with light. What happens to the EM field? 6. We don’t ordinarily notice photons. Suppose that Planck’s constant were much larger than it actually is. Would we then be more likely, or less likely, to notice photons? 7. Which has higher energy: a photon of red light or a photon of yellow light? 8. Which has lower energy: a photon of ultraviolet radiation, or a photon of infrared radiation? 9. In the double-slit experiment with light, are tiny photons actually coming through the slits? What is coming through the slits? 10. When we greatly dim the light used in a double-slit experiment, we don’t simply get a dimmer interference pattern. What do we get? 11. A red light beam has a variable intensity, or brightness. As you increase the intensity, do the energies of the individual photons increase, decrease, or remain the same? 12. In the preceding question, does the number of photons emitted each second increase, decrease, or remain the same? 13. A red light beam has a variable frequency. As you increase the frequency, does the color change? Do the energies of the individual photons increase, decrease, or remain the same? 14. In the preceding question, do the speeds of the photons change? 15. What kind of waves are demonstrated by the experimental result shown in Figure 13.2? Waves in what (what is the medium called)? Electron Interference and the Quantum Mystery of Matter 16. What kind of waves are demonstrated by the experimental result shown in Figure 13.9? Waves in what? 17. Which has a shorter wavelength, an electron or a proton moving at the same speed? 18. Which has a shorter wavelength, a slow electron or a fast electron? 19. Suppose that we use a very low intensity beam in the double-slit experiment with electrons, so low that only one electron appears per minute. Will we see an interference pattern on the screen? What will we see? 20. List some similarities between an electron beam and a light beam. 21. List some similarities between an electron and a photon. 22. List some differences between an electron and a photon. 23. The impact point of each electron is unpredictable in the double-slit experiment with electrons. What is predictable? 24. If an electron traveling through a double-slit apparatus strikes directly behind slit A, is it correct to say that the electron came through slit A? 25. If electrons behaved only like particles and not like waves, would you observe an interference pattern in the double-slit experiment? 26. You don’t notice the wave aspect of a pitched baseball. Is this because the baseball’s wavelength is very long or because it is very short? 27. Arrange these in order from shortest to longest wavelength, assuming that they all have the same speed: helium atom, automobile, DNA molecule, electron, neutron, baseball. 28. If a “proton microscope” could be devised, how would you expect its wavelength to compare with the wavelength of an electron microscope. Quantum Uncertainty 29. When you flip a coin, the outcome is uncertain. Does this arise from quantum uncertainty? Explain. 30. What is the percentage probability of getting two heads in a row in fair coin tosses? How could you experimentally test this prediction? 31. In the double-slit experiment with electrons, is the impact point predictable? 32. In the double-slit experiment with electrons, are there any points where we can predict that an electron will certainly not hit? 33. What is predictable in the double-slit experiment with electrons? 34. Would the answers to the preceding three questions be different if we were talking about photons instead of electrons? 35. List at least two differences between Newtonian physics and quantum physics. 36. List at least two similarities between Newtonian physics and quantum physics. problems The Quantization of Light 1. A light source emits two colors simultaneously: orange and violet. Which color has the higher energy per photon? 2. In the preceding problem, the frequencies are (orange) and (violet). Find the energies of the photons. 3. Which has greater energy, a microwave photon or a visible photon? About how many times greater (consult Figure 9.5)? 4. You charge an object by rubbing it, and then shake it at 1 Hz, creating EM radiation. How much energy does each photon carry? 5. How much energy does one photon of gamma radiation carry? 6. Making estimates. About how many visible photons would be needed to have enough energy to lift a 1 newton (about 1/4 pound) weight through 1 meter (consult Figure 9.5)? 7. Making estimates. About 10 visible photons are needed to cause a single photosynthesis reaction in living plants. About how much energy is carried by these 10 photons? 8. Making estimates. The human eye can detect as few as 10,000 photons per second entering the pupil. About how much energy is this per second? The Waviness of Matter 9. If you double the speed of a proton, how does this affect its wavelength? 10. How would the wavelength of a proton compare with the wavelength of a deuteron (a proton and neutron held together by nuclear forces), assuming that both the proton and the deuteron have the same speed? 11. An electron and a proton are moving at the same speed. Which has the longer wavelength? How much longer? (Protons are about 1800 times more massive than electrons.) 12. Suppose we fire a high-velocity pellet gun that accelerates 1 gram pellets to speeds of 1000 m/s (three times the speed of sound). Find the wavelength of the pellet’s matter wave. 13. Find the wavelength of an electron that strikes the back of a TV screen at a speed of 0.1c. The mass of an electron is 14. Individual electrons have been slowed down to speeds as low as several centimeters per second. The mass of an electron is What is the wavelength of a single electron moving at 0.1 m/s (10 cm/s)? Express your answer in millimeters. 15. In a recent experiment, sodium atoms were cooled until they were moving at only a few meters per second. The mass of a sodium atom is What is the wavelength of a single sodium atom moving at 2 m/s? Express your answer in millimeters.