The metre is defined as the distance travelled by light in 1/299,792,458 second. Why didn't people choose some easier number such as1/300,000,000 second? Why not 1 second?

Asked by  | 21st May, 2012, 10:28: PM

Expert Answer:


If we have to define any quantity, we start from unity. If we have to define time, we first need to define 1 unit time. If we define length, we first need to define 1 unit length. If we define time we need to define 1s. We can define second as the time taken by a man moving with velocity 3m/s to cover 3 meter.

Light travels at a speed of 299792458 m/s in vacuum. If we take a quantity of time as 1/299792458 s. We get distance covered as:


This unity value with dimension [L] was given a unit for measurement meter and thus was defined by the distance covered by light in 1/299792458 s. If we would have taken 300000000 s. We would get an answer in fraction and if we would have taken 1s we would get a length equal to the speed of light. But, as we know that we define a unit with unity, meter would never have been defined and we would not be measuring length in mm, cm, m or km.

Answered by  | 22nd May, 2012, 10:19: AM

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