Tuesday, June 14, 2005
Speed of light
Question:
The speed of light calculated in 1977 was 299,792,457.6 m/s. After 1983 it is 299,792,458 m/s exactly, how could that be?
Hints:
At the 1983 General Conference on Weights and Measures they decided that since they have a definition of the second, they should define the meter as how far light in a vacuum can travel in that second. Using lasers and accurate clocks today allows us to calculate the speed of light very accurately. Before the length of a meter was defined by a bar in
Before (since 1791) the definition of a meter was 1/10 millionth of the length of the meridian of the earth along a quadrant. i.e. 1/40 millionth the circumference. This was not precise enough, so they made a new definition.
Links:
Magic Dave
Length Conversion Table.
The speed of light calculated in 1977 was 299,792,457.6 m/s. After 1983 it is 299,792,458 m/s exactly, how could that be?
Hints:
- A second is now defined as x many transitions of a Cesium-133.
At the 1983 General Conference on Weights and Measures they decided that since they have a definition of the second, they should define the meter as how far light in a vacuum can travel in that second. Using lasers and accurate clocks today allows us to calculate the speed of light very accurately. Before the length of a meter was defined by a bar in
Before (since 1791) the definition of a meter was 1/10 millionth of the length of the meridian of the earth along a quadrant. i.e. 1/40 millionth the circumference. This was not precise enough, so they made a new definition.
Links:
Magic Dave
Length Conversion Table.
# posted by Scott Kirkwood @ 11:26 AM 
