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Physics A: Problem Set 15: The nature of light

recommended reading

High Marks: n/a
Barron's Let's Review: 12.1–12.4
physics.info: The nature of light
Wikipedia: Light, Speed of light, Visible spectrum
HyperPhysics: Speed of light, Visible light
Khan Academy: Introduction to light waves
YouTube: Roy G. Biv
Mr. Machado: 15 Wave Phenomena - From Sound to Light

homework

  1. Using the Reference Tables for Physical Setting/PHYSICS, determine the color of the 9 different light waves below with the following characteristics:
    1. A frequency of…
      1. 4.30 × 1014 Hz
      2. 5.63 × 1014 Hz
      3. 6.34 × 1014 Hz
    2. A wavelength of…
      1. 4.21 × 10−7 m
      2. 4.73 × 10−7 m
      3. 5.87 × 10−7 m
    3. A period of…
      1. 1.78 × 10−15 s
      2. 1.96 × 10−15 s
      3. 2.03 × 10−15 s
  2. Autonomous cars use lidar to determine the distance to objects around them using pulses of laser light. The word lidar is an acronym of light detection and ranging and was intended to mimic the words radar (radio detection and ranging) and sonar (sound navigation and ranging). A detector near the laser measures the time between when a pulse was sent out and when a reflection was received back. Some systems also compare the wavelength of the reflected laser light to the wavelength transmitted. Optical data for one particular lidar system are given in the table below.
    Automotive lidar system
    characteristic value
    wavelength905 nm
    pulse duration3 ns
    pulse power8 W
    beam divergence0.12°
    1. What type of electromagnetic radiation does this laser emit?
    2. What is the energy in one pulse of this laser?
    3. If the time of flight for one pulse to hit an object and return is 40 ns, how far away is the object from the car?
    4. If the reflected laser light has a wavelength of 904.99994 nm, what additional information does this tell you about the distance between the object and the car?