A device that uses a hyperfine transition frequency in microwave or electron transition frequency in the optical or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element is known as atomic clock. The atomic clock shows the most accurate time and frequency standard known and are used as the primary standard for international time distribution service. It is there to control the wave frequency of tv broadcasts, and in global navigation in the satellite system.
The atomic clocks operation principle is based on atomic physics, it measures the electromagnetic signals that electrons in atoms emit when they change energy level.
Measurement of Time
Time is defined as the interval between two events. The science and study of time measurement is known as horology or chronometry. Chronology is defined as science of arranging events in sequence or order of occurrence in time, and is mainly used for studying the paste time or the history. Periodic events are defined as the events which repeat after the same and equal interval of times motion of sewing needle of machine and bob of simple pendulum are few of the examples. In our daily use we use the 12 hour time system whereas airlines and railways use the 24 hours clock system. Time can be measured in many ways by using a simple pendulum, atomic clock or stopwatch. Two basic components are exhibited in two ways:
A means of keeping track of increment of ways of displaying the results or increment of time.
A regular, repetitive or constant action to mark of equal increment of time.
Based on the rotation of the earth the oldest and the most used method of measuring time is based due to which day and night occurs. The sun setting and the sun rising are considered as the periodic motion and are considered as the reference for measuring time. Earlier people used to bifurcate the day into two parts: the day part and the night part, but now due to the development of science and more and more social interactions there was a need to divide the day more precisely. The modern convention states that a day is divided into 24 hours and 1 hours is divided into 60 minutes and a minute is divided into 60 seconds.
Unit of Time
A midst unit or the unit of time is defined as any particular time interval which is used as a standard way of measuring or expressing duration. In the international system of unit and extension of the western world in the base unit of time is the second defined as about 9 bellion oscillations of caesium atoms. The National institute of standard technology defines it as: the duration of 9192631770 periods of the radiation corresponding to the transition between the 2 hyperfine levels of the ground states. Earlier the unit of time was defined by movements of the astronomical objects. In the past time the time was decided by the sun then after sun it was defined by moon the the earth and then celestial spheres.
Most historical societies used natural units for time keeping; they used the sun, solar year, lunation, days etc. such calendar includes the Egyptian, Chinese, Ancient Athenian, Buddhist, Hindu, Islamic, Icelandic, Mayan etc.
What is Time Period of Pendulum
A simple gravities pendulum period of swinging depends on its length, the local strength of gravity, and to the small extent on the maximum angle that the pendulum swings away from vertically which is known as the amplitude. It’s independent of the bob's mass. If the amplitude is limited to the small wings then the period of small pendulum that is T the time taken for the complete cycle.
One of the very early uses of a pendulum was in the 1st century seismometer device of Han dynasty Chinese scientist Zhang Heng. It's function was to activate and sway one of the series of levers after being disturbed by the tremor of an earthquake far away.
The Atomic Clock
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In the year 1879 the idea of using atomic transitions to measure time was suggested by lord kelvin. In 1930 the magnetic resonance was developed by Isidor Rabi. It became a particle method of doing this. Rabi first publicly suggested in 1945, that atomic beam magnetic resonance might be used as the basis of clocks. The very first atomic clock was the ammonia absorption line at 23870. The U.S.A based national bureau of standard has less accuracy than the quartz clock, but it served to demonstrate the concept. A Cesium based atomic clock or the first accurate atomic clock, was based on a certain transition of cesium-133 atom. It was built by Louis Essen and Jack Perry in 1955.
The cesium standard calibration standard atomic clock was carried out by the use of the astronomical time scale ephemeris time (ET). This led the scientific community to redefine in 1967, the second in terms of specific atomic frequencies.