Question

One second is defined as

• A. 1650763.73 periods of krypton clock
• B. 652189.6 periods of krypton clock
• C. 1650763.73 periods of cesium clock
• D. 9192631770 periods of cesium clock

Answer 1

Answer: (D)

9192631770 periods of cesium clock

The second is the duration of $9192631770$ periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium$-133$ atom.