Section 1 review
Light is a traveling transverse wave in an oscillating electric and magnetic field. The speed of light in a vacuum is a constant at 3×108 m/s. The colors of visible light are directly related to the wavelength of the light. Light can be scattered by small particles, but scattering of light waves depends on the relative sizes of the particles and the wavelength of the light. This is similar to the idea that long-wavelength water waves can easily pass around small boulders but short-wavelength water waves cannot. Scattering of light is the explanation for why the daytime sky is blue and sunsets are red. Read the text aloud
light, electromagnetic wave, speed of light, vacuum, scattering

c=fλ

Review problems and questions

  1. Use a diagram and describe with words the connection between the field of an electric charge and light waves. Read the text aloud Show
  1. Lightning strikes a tree one mile (1.609 km) away from you. Light from the lightning bolt travels at 3×108 m/s while sound waves from the accompanying thunderclap travel at about 343 m/s.
    1. How long does it take the light to reach you?
    2. How long does it take the sound of the thunderclap to reach you?
    3. Formulate a simple rule for estimating the distance to a lightning strike. Read the text aloud Show
  1. How are electromagnetic waves similar to sound waves? How are they different? Read the text aloud Show
  1. How are the electric and magnetic fields in an electromagnetic wave related to each other? Read the text aloud Show
  1. Which has higher frequency, cyan light or yellow light? Read the text aloud Show
    1. What is the frequency of light with a wavelength of 560 nm?
    2. An angstrom (Å) is 10−10 m. What wavelength, in nanometers, corresponds to 6,563 Å?
    3. What is the wavelength of light corresponding to 121.5 MHz?
    4. Which has a higher frequency, light with a wavelength of 1.7 μm or light with a frequency of 7.3×1013 Hz? Read the text aloud Show
  1. Imagine looking up at the night sky. If you look in any given direction at a tiny patch of sky, you will eventually come across a star or galaxy. That little patch of sky would then appear white. The German astronomer Heinrich Wilhelm Olbers in 1823 described this as a paradox: Why is the night sky black instead of white? Offer an explanation to resolve this paradox. Read the text aloud Show
  1. If we were on a planet—or moon—that had no atmosphere, what color would the daytime sky be? Read the text aloud Show

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