Light Properties Printer Friendly Version
Refer to the following information for the next three questions.

The first investigation that led to a determination of the speed of light was performed in about 1675 by the Danish astronomer Olaus Roemer. He made careful measurements of the period of Io, a moon about the planet Jupiter, and was surprised to find an irregularity in Io's observed period. While the earth was moving away from Jupiter, the measured periods were slightly longer than average. While the earth approached Jupiter, they were shorter than average. Roemer estimated that the cumulative discrepancy amounted to about 16.5 minutes. Later interpretations showed that what occurs is that light takes about 16.5 minutes to travel the extra distance across the earth's orbit. Aha! We have enough information to calculate the speed of light!
 What is the diameter, in meters, of the earth's orbit around the sun?

 According to Roemer, about how many seconds does it take light to travel across the diameter of the earth's orbit?

 How do these two quantities determine the speed of light?

Refer to the following information for the next four questions.

Study a chart of the electromagnetic spectrum (link) and answer the following questions.

Which has the longer wavelengths, radio waves or waves of visible light?
Which has the longer wavelengths, waves of visible light or gamma rays?
Which has the higher frequencies, ultraviolet or infrared waves?
Which has the higher frequencies, ultraviolet waves or gamma rays?
Refer to the following information for the next seven questions.

Carefully study the behavior of light through transparent materials (link) and answer the following questions.
 When ultraviolet light shines on glass, what does it do to electrons in the glass structure?

 When energetic electrons in the glass structure vibrate against neighboring atoms, what happens to the energy of vibration?

 What happens to the energy of a vibrating electron that does not collide with neighboring atoms?

Light in which range of frequencies, visible or ultraviolet, is absorbed in glass?
Light in which range of frequencies, visible or ultraviolet, is transmitted through glass?
 How is the speed of light in glass affected by the succession of time delays that accompany the absorption and re-emission of light from atom to atom in the glass?

 How does the speed of light compare in water, glass, and diamond?