Q. Ins is defined as
A) $10^{- 9}\ s\ of\ Kr - clock\ of\ 1650763.73\ oscillations\$
B) $10^{- 9}\ s\ of\ Kr - clock\ of\ 6521389.63\ oscillations\$
C) $10^{- 9}\ s\ of\ Cs - clock\ of\ 1650763.73\ oscillations\$
D) $10^{- 9}\ s\ of\ Cs - clock\ of\ 9192631770\ oscillations\$
Explanation
The second is the duration of 9192631770 period of the radiation corresponding to the transition between the two hyperfine levels of the ground state of cesium-133 atom. Therefore, 1 ns is $10^{- 9}\ s$ of Cs-clock of 9192631770 oscillations.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.