Class 11 Physics Units and Measurements Measurement of Time

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.

  • 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.
  • Cesium clocks are very accurate and the uncertainty is very low 1 part in 1013 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

Period of radio wave

10-6

Period of sound wave

10-3

Wink on an eye

10-1

Travel time of light from moon to earth

100

Travel time of light from sun to earth

102

Rotation period of the earth

105

Revolution period of the earth

107

Average human life span

109

Age of Egyptian pyramids

1011

Time since dinosaur extinction

1015

Age of Universe

1017

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