- Second
Dear students we know that, time is most important fundamental quantity. From ancient ages, the measurement of time had the most curious thing to do. Before few centuries the measurement of time was done with the sky observation, .i.e the observation of sun, moon, stars etc which measured the time according to seasons, changes in position of moon. In modern era time was measured with the help of clocks like sundial, water clock, sand clock etc. The time was measured in some conventional units/forms as year, month, week etc. After discovery of quartz crystal the measurement of time become more convenient and accurate.
In modern science, the unit of time is taken from the study of vibration of crystals. SI unit of time is taken from the vibrations of caesium atom (133Ce). The time taken by caesium atom to complete almost 9 billion of vibrations is termed as ‘second’
Exact meaning of 1 second time can be defined as the fixed numerical value of the caesium frequency, ΔνCs, stable and the ground-state hyperfine transition frequency of the caesium 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s−1.
Hence the SI unit of time is ‘second’ and its symbol is ‘s’.
Following are the some scientific based unit used for measurement of time,
- Planck time, i.e. The amount of time light takes to travel one Planck length = 39×10−44 s
- Jiiffy, The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum = 10−24s
Important Faq on SI unit of Time
Q.1) What is megaanum or mega year?
Answer: This unit of time is related to studies of galaxies.
Megaanum or mega year = 106 year
It is also called as millennia.
Q.2) What do you mean by Gregorian year and lunar year?
Answer: The Gregorian year is used in formation of modern calendar where,
1 Gregorian year = 365 days 5 hours 49 min 12 sec
Whereas lunar year is the time to complete 12 full cycles of the moon around the earth.
1 Lunar year = 354 days
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