Many physicists are witty and insightful. The famous physicist Enlik Fermi once said that the standard lecture time (50 minutes) approximated a microcentury. So, do you know exactly how long a microcentury is? To solve this problem, we need to know not only the concept of time (physical quantity), but also how much the "cap" (prefix) in front of the unit becomes.
The international System of units (symbol SI, better known as the metric system) was adopted in 1960 by the 11th International Congress of Metrology (whose executive body is the International Bureau of Measurement). In the SI system of units, units are divided into three categories: basic units, derived units and auxiliary units. The seven strictly defined basic units are length (meter), mass (kilogram), time (second), current (ampere), thermodynamic temperature (kelvin), quantity of matter (mole), and luminescence intensity (Candela). The basic units are dimensionally independent of each other. There are many derived units, all of which are composed of basic units.
In addition, there are 20 SI prefixes specified in the SI system for forming multiples of SI units.
Now let's calculate how many minutes a micro century is: "micro" represents 10-6 times, "1 century" is 100 years, a year is 365 days, a day has 24 hours, 1 hour corresponds to 60 minutes, so: 1 micro century =10-6x100x365x24x60=52.56 minutes. Do you understand Fermi now?
Measurement of time
A (mechanical) stopwatch is often used to measure time in high school physics classes.
Any phenomenon that repeats itself is a measure of time. In ancient China, people used to time the clock with a constant water level in one container, and the liquid level was raised by pouring water through the channel into another container, and the liquid made the float rise to indicate the time. Shen Kuo of the Northern Song Dynasty of China tried to reduce the error caused by the influence of temperature on viscosity, so that the timing of high precision. Galileo discovered the periodicity of the pendulum, and Huygens of Holland invented the escapement to keep the pendulum swinging, making it possible to use the phenomenon of pendulum periodicity to keep time. Accurate pendulum clocks for laboratory use have been refined to an error of only a few seconds a year. In the early 20th century, people began to use the piezoelectric effect of quartz crystal timing, the so-called piezoelectric effect refers to the crystal can transform mechanical deformation oscillation into electrical oscillation, by the 1940s, quartz crystal timing has developed into the main standard of timing, with an error of about 0.1 millisecond per day.
World's first cesium atomic clock (NATIONAL Physical Research Institute, 1955)
Atomic clocks were developed to meet higher time standards. An atomic clock at the U.S. National Bureau of Standards and Technology in Colorado was established as the standard for Coordinated Universal Time (UTC). In 1967, the 13th International Metrology Conference defined the cesium-133 atomic clock as the standard of the second: the duration of 9192631770 cycles of radiation corresponding to the transition between the two hyrefined energy levels of the cesium-133 atom in the ground state is 1 second. Normally, two cesium clocks will differ by less than a second after 6,000 years of operation. A clock with a more accurate internal structure is still in development.
Beijing time, as adopted in China, is determined and maintained by the National Time Center of the Chinese Academy of Sciences in Xi 'an, Shaanxi Province.
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