Measuring Speed of Light - Foucault's Method
This section describes the method used by Léon Foucault to measure the speed of light using using a rotating mirror and a fixed mirror.
In 1857, the French physicist Léon Foucault enhanced Fizeau method
to measure the speed of light using a rotating mirror and a fixed mirror,
as illustrated in the picture below.
Foucault's measurement is based on the following idea:
- Light coming from the source hits a rotating mirror.
- The rotating mirror reflects the light to a fixed mirror
at a far distance (like 8,000 m).
- Then fixed mirror the light back to rotating mirror.
- This backward light will be bounded off the rotating mirror
towards the light source with a small angle caused by the rotation.
This angle can be used calculate the speed of light.
Using this idea, Foucault was able to measure the speed of light as 299,796,000 m/s.
This is very close to today's definition of the speed of light: 299,792,458 m/s.
Last update: 2014.
Table of Contents
About This Book
Introduction of Space
Introducion of Frame of Reference
Introducion of Time
►Introduction of Speed
What Is Speed?
List of Various Speeds
Different Speeds Observed in Different Frames
Measuring Speed of Light - Roemer's Method
Measuring Speed of Light - Fizeau's Method
►Measuring Speed of Light - Foucault's Method
Newton's Laws of Motion
Introduction of Special Relativity
Time Dilation in Special Relativity
Length Contraction in Special Relativity
The Relativity of Simultaneity
Introduction of Spacetime
Minkowski Spacetime and Diagrams
PDF Printing Version