Define the $SI$ unit of force,the newton $(N)$. Define the $CGS$ unit of force,the dyne.

The new $SI$ unit of mass $1 \, kg$ is defined in terms of the difference in the masses of two ${}^{133}Cs_{55}$ atoms. One of these atoms is in its ground state and the other is in an excited state that has a frequency of excitation close to $9.2 \times 10^9 \, Hz$. The number of atoms required to get $1 \, kg$ of mass this way is of the order of (Planck's constant = $6.63 \times 10^{-34} \, J \cdot s$; mass of proton = $1.67 \times 10^{-27} \, kg$; Avogadro number = $6.02 \times 10^{23} \, \text{particles}$; speed of light = $3 \times 10^8 \, m/s$).

In a cesium clock,the time interval depends on which factors?

How many light-years are in $1$ parsec? And how many astronomical units are in $1$ light-year?

$Parsec$ is a unit of

One femtometer is equivalent to