CBSE-XI-Physics
01: Introduction to Physics
- #1The metre is defined as the distance travelled by light in
1\ 299,792,458 second. Why didn’t people choose some easier number such as
1\ 300,000,000 second? Why not 1 second?Ans : The speed of light in vacuum is 299,792,458 m/s.
Then time taken by light to cover a distance of 1 metre in vacuum = `` \frac{1}{299,792,458}`` s
Hence, the metre is defined as the distance travelled by light in `` \frac{1}{299,792,458}`` s.
As 300,000,000 m/s is an approximate speed of light in vacuum, it cannot be used to define the metre.
The distance travelled by light in one second is 299,792,458 m. This is a large quantity and cannot be used as a base unit. So, the metre is not defined in terms of second.