If you've seen a ruler used in primary and secondary schools, it is likely that the length of 30 cm ruler. Thirty centimeters is approximately equal to 12 inches or 1 foot (foot, is a unit of length ala the British Empire). Has it occurred to you guys in mind, the reason why the length of 30 cm ruler lebish often?
In the field of computers and electronics, a length of 30 cm has a special meaning. Special meaning is important and to be hold in designing and building a series of microelectronics and integrated circuit (integrated circuit, IC).
approximately 30 cm is the distance traveled by the electromagnetic waves within a billionth of a second. The period of one second per billion corresponds to a frequency of 1 billion cycles (cycles) per second (giga hertz, GHz), so more or less on the order / scale equal to the speed of today's computers.
Factor 30 cm to be important in designing an electronic circuit that operates at GHz frequencies. In the GHz scale electronic circuits, cycle electric current in the circuit will produce an electromagnetic wave that has a length at about the scale of centimeters.
If the electronic circuit is also on the scale of centimeter-sized, the engineer who designed the circuit must consider the time factor required for the propagation of electromagnetic waves in series.
similar problem, namely factor in the time required for the propagation of electromagnetic waves, appearing in many everyday technology: radar, satellite and mobile telecommunications, optical fiber networks (optical fiber), global positioning system, mapping, geodesy, and more .
In particle physics experiments, this problem arises when physicists must consider the travel time of the signal in an optical fiber detector located 100 meters below ground to a computer that reads and stores the data on the ground.
example, the LHC accelerator operates with a frequency of 40 MHz or a 25 per billionth of a second. Every 25 a billionth of a second, there were several collisions / interactions in the detector. Using the rule of 30 cm, we know that over 25 per billionth of a second, the light will travel a distance of 7.5 meters.
Though the distance from the basement to the ground level is 100 feet! Before the signal reaches the surface of the detector and recorded in the computer, the detector has received the data back.
use size 30 cm to provide an illustration / picture of the speed of light and the distance, popularized by First Admiral (Commodore / Rear Admiral) Grace Hopper, an elder in computer science and informatics.
