IIT JEE Measurement of Time | JEE General Physics Measurement and Time

Definition of Measurement of Time

Time is defined as the period in which a process, action or an event takes place. Time is also called the Point or Period when something occurs. Time is an integral part of Physics and every single quantity in the physical world relies on it. Time has made the universe function in a simple and routine way. If time wouldn’t have existed, there would be many irregularities in schedule and timing of people. It is quite difficult to think of life when there is no time. There won’t be any physical quantities like acceleration, velocity and electromagnetic waves which depend on time for their existence.

Time

Image 1: National Physical Laboratory maintains the standard time of India using 4 atomic clocks

To measure a time interval we need a clock. Clocks in India works on the atomic standard of time, which is based on the periodic vibrations produced in a Cesium atom. That’s why Indian clocks are also called Cesium Clock. The standard unit of time is second.

Before the invention of atomic clocks, people used to measure time by observing daily durations of the day. People used to divide their lifestyle into three-time durations namely morning, afternoon and evening times. The need to develop clock came into form when people got confused with time-intervals and daily schedules as in winter and rainy seasons they can’t get their time durations assigned. Then after the invention of clocks, the time was divided into smaller sections to ensure quality work by people.

Second

Image 2: Earlier people used to see time using hourglass

Second is the universally accepted unit of time. 1 second is defined as the time taken for 9,192,631,770 vibrations of the radiation relative to the transition between two levels of ground state of Cesium-133 atom.

Image 3: Symbol of NPL

The vibrations in atomic or cesium clock are same as those in quartz clock which is mostly used in wrist watches. The Cesium atomic clocks are very accurate and long lasting. The Indian standard of time “second” is conserved by four Cesium atomic clocks. NPL or National Physical Laboratory in New Delhi is authorized to maintain the Indian standard of time using Cesium clocks.

NPL in India manages time standards and address improvement in physical standards like frequency, time etc. The IST or Indian Standard Time is also linked to set of four atomic clocks in NPL to maintain the time of the country in a good accurate manner. The error in atomic size is of the order 10-13, which is very less.

Range of Time

Image 4: We use certain units to measure time

Just like other physical quantities, the range of time is also quite vast and varies fundamentally from the microscopic level to the macroscopic level. The table given below depicts various range and order of time intervals.

 Event or Condition Time interval (s) Lifespan of most unstable particle 10-24 Time to cross a nuclear distance 10-22 Period of atomic vibrations 10-15 Period of X-rays 10-19 Period of light wave 10-15 Life of atom in an excited state of an atom 10-8 Period of radio wave 10-6 Period of sound wave 10-3 Blink of eye 10-1 Time between two successive heartbeats 100 Time taken by light to travel from the moon to the Earth 100 Time taken by light to travel from Sun to the Earth 102 Time period of a satellite 104 Rotation period of the earth 105 Rotation and Revolution period of the Moon 106 Time taken by the Earth for 1 complete revolution 107 Time taken by a light to reach earth from a star 108 Average Human Life 109 Age of Egyptian Pyramids 1011 Age of the world 1017

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Measurement of Time

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