Contents

# Contents

## Idea

The second is a physical unit of time. It is defined by taking the fixed numerical value of the caesium frequency $\Delta \nu_{Cs}$, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be $9192631770$ when expressed in the unit $Hz$, which is equal to $s^{-1}$

## References

Last revised on April 2, 2019 at 19:57:24. See the history of this page for a list of all contributions to it.