Measurement of Time
Time is measured using a clock. As a standard, atomic standard of time is now used, which is measured by Cesium or Atomic clock.
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In Cesium clock, a second is equal to 9,192,631,770 vibrations of radiation from the transition between two hyperfine levels of cesium- 133 atom.
Cesium clock works on the vibration of cesium atom which is similar to vibrations of balance wheel in a regular wristwatch and quartz crystal in a quartz wristwatch.
National standard time and frequency is maintained by 4 atomic clocks. Indian standard time is maintained by a Cesium clock at National Physical Laboratory( NPL), New Delhi.
o Cesium clocks are very accurate and the uncertainty is very low 1 part in 10 13 which means not more than 3 μs are lost or gained in a year.
Range of Time Event Time Interval( s)
Life span of most unstable particle 10-24
Period of x-rays 10-19
Period of light wave 10-15