The SI second is defined using a property of one particular kind of atom. Which one?
Uranium 235
Hydrogen
Caesium 133✓پاسخ درست
Carbon 12
توضیح
The second is fixed by giving the hyperfine transition frequency of the caesium 133 atom the exact value 9 192 631 770 hertz. One second is the time taken by that many cycles of the corresponding radiation.