What is the speed of light?
The speed of light in vacuum is exactly 299,792,458 m/s (metres per
second)
In 1983 the SI (Systeme International) defined a metre as:
- The metre is the length of the path travelled by light in vacuum
during a time interval of 1/299 792 458 of a second.
When people refer to the speed of light, they refer to the definition
above - the speed of light in a vacuum.
The speed of light is normally rounded to 300 000 kilometers per second
or 186 000 miles per second.
The speed of light depends on the material that the light moves through
- for example: light moves slower in water, glass and through the atmosphere
than in a vacuum. The ratio whereby light is slowed down is called the
refractive index of that medium.
In general, the difference in the speed
of light in other mediums is ignored. |
