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Diffraction and Interference Practice Questions

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Updated on Sep 27, 2011

Review these concepts at: Diffraction and Interference Study Guide

Practice Questions

  1. Consider two sources emitting waves and two waves meeting in a region of space. The wave diagram is shown in Figure 20.5. What is the result of the superposition of the two waves?

    Superposition Principle

  2. Consider the following two waves. What are the amplitude, the frequency, and the wavelength of each wave? Also, find the result when the two waves are at the origin of time and space
  3. Two screens each have an aperture; one is 550 nm and the other one is 0.600 μm. Which one will produce on a screen a broader fringe pattern if illumination with a blue light of 430 nm is used?
  4. Is it fair to say that no bending of light occurs through an open door, but diffraction occurs when you shine a laser light through the measuring part of a micrometer?
  5. A screen is in front of a 0.95 μm aperture. Find the distance to the position of the first dark fringe if a 690 · 10–9 m light is shone on the aperture and the position of the dark fringe is 20 cm away from the bright central of the image.
  6. The width of the bright central fringe on a screen is 18 cm and the light that forms it is a blue 400 nm. The light is shown on a 0.80 μm aperture. Find the distance to the screen.
  7. Laser light is a monochromatic light (one color and one characteristic wavelength). For instance, the helium-neon laser produces a 632.8 nm red light and the solid-state green laser 532 nm. Therefore, the fringe pattern will be composed of dark and one-color light fringes. What do you think a white light fringe pattern will look like? Why?
  8. White light is directed toward a diffraction grating and that light splits into monochromatic principal maxima. Which color will be closer to the central white?
  9. Is it possible for unpolarized light to "disappear" after it propagates through a system of polarizer and analyzer?
  10. Is it possible for unpolarized light to emerge from a system of one polarizer and one analyzer with the same intensity in which it went in?
  11. Is the process of polarization characteristic only for light waves? How about the other electromagnetic waves?
  12. Incident light is entering a system of three polarizers with an intensity of 2 kW/m2. The angles for each of the polarizers are θ1 = 60°, θ2 = 90°,θ3 = 30°. What is the average intensity of the outgoing light?
  13. Incident light is entering a system of three polarizers with an intensity of 2 kW/m2 . The angles for each of the polarizers are θ1 = 60°, θ2 = 45°,θ3 = 30°. What is the average intensity of the outgoing light?

Answers

  1. A wave with the same frequency and double amplitude
  2. A1 =20 cm, A2 = 23 cm, λl = 5.7 · 10–10 m, λ2 = 6.7 · 10–10 m, f1 = 0.32 Hz, f1 = 0.03 Hz, y1 + y2 = 43 cm
  3. The 550 nm will give a larger diffraction pattern.
  4. Yes, the size of the door opening is so much larger than the wavelength of light while a micrometer can open a few micrometers (or the equivalent of a hundred nanometers, the range of light wavelength).
  5. d = 27 cm
  6. L = 16 cm
  7. Each component color of light will diffract differently because the bending is directly proportional to the wavelength: the central is a bright white followed by the rainbow colors bright maxima and in between the dark fringes.
  8. The one with least diffraction: violet
  9. Yes, if the transmission axes are perpendicular on each other.
  10. As noted in the lesson: The average intensity of light leaving the polarizer is half of the intensity of the incident light.
  11. For all electromagnetic waves, we can define polarization because the same principle of electrical current variation applies to all.
  12. It will be zero because the second polarizer is at 90° with respect to the first one.
  13. S = 0.375 kW/m2
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