Module 5
1. Module 5
1.11. Page 4
Module 5—Wave Theory of Light
Lesson Summary
At the start of this lesson you were asked the following essential questions:
- How can you measure the speed of light using another planet?
- How can you measure the speed of light in a laboratory?
- How can you measure the speed of light using a microwave oven?
The earliest attempts to accurately measure the speed of light involved astronomical distances. The periodic eclipse of Jupiter’s moon, Io, provided the first reasonable estimate for the speed of light in a vacuum.
Years later, a more accurate measurement of the speed of light was performed by Albert Michelson. In his apparatus, a rotating mirror was used to reflect light to and from a distant mirror, allowing the measurement of very small time intervals based on the periodic rotation of an eight-sided mirror. Given data about the period of rotation and the distance separating the rotating and fixed mirror, it is possible to determine the speed of light using v = d/t.
In other experiments it is possible to measure the wavelength of EMR based on a standing wave pattern, such as the one that exists in a microwave oven. Given the wavelength and frequency, it is possible to determine the speed of light using the universal wave equation, c = fλ.
Given that light and all other classifications of EMR travel at a constant speed in air or in a vacuum, it is possible to develop precise technologies for measuring both terrestrial and astronomical distances.