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