sdfgh ime In 1967, a new standard was adopted for the definition of the second (SI unit of time). It is based on an atomic clock, which uses the energy difference between the two lowest energy states of the caesium atom. When bombarded by microwaves of precisely the proper frequency, caesium atoms undergo a transition from one of these states to the other. One second is defined as the time required for 9192631770 cycles of this microwave radiation. The time interval between sdftwo events is the difference between the times when the events occurred. When the time interval is of the order of minutes or hours, clocks and watches can be used. For shorter time intervals of the order of seconds, stop clocks or stop watches are used. These have devices for starting and stopping as well as for setting them to zero before timing is commenced. Fractions and multiples of the second are given below: 1Time