What is the advantage of the SI unit over CGS units?
Answers
Answer:
CGS is actually a family of systems of units—there are electrostatic CGS units, electromagnetic CGS units, Gaussian CGS units, and yet others that are less popular variants. There is only one SI to keep straight—a huge advantage.
CGS units cover only mechanics and electromagnetism using a 3-dimensional system. SI has separated out electromagnetism from mechanics to make a 4th dimension, and has built in to the system coverage of temperature, amount of chemical substance, and quantities involving illumination to yield a 7-dimensional system. Thus, SI has far more coverage of physical quantities built in to the system than CGS does.
Both the SI and the CGS systems are coherent. However, SI provides a set of scaling prefixes to apply to the root name of units that gives you a choice of tradeoff—work with nice numbers by using the prefixes that have the drawback of not being coherent versus work with only the coherent units and potentially need to work with very large or very tiny numbers. CGS is strictly coherent by not providing any extra prefixes—all lengths must be in terms of centimeters, never millimeters, meters, nor kilometers. The diameter of a proton can be expressed in SI as either 1.7 fm or 1.7 × 10⁻¹⁵ m, whereas CGS requires expressing as 1.7 × 10⁻¹³ cm (or you write 0.000 000 000 000 17 cm and similarly for SI). The greater flexibility of SI gives it an advantage. A similar situation occurs for much larger lengths, such as the diameter of a star. It is especially entertaining to read articles about the rate of stellar energy output in ergs per second.
In everyday life, electrical engineering, and experimental physics, it is almost always the case that the SI units of electromagnetism are used, not CGS units. A significant part of the problem is that electromagnetic units cannot be truly converted between any of the CGS units of any flavor and SI units—there is only a correspondence. This arises because there is no base unit of electromagnetism in CGS, because all units of electromagnetism are derived from the centimeter, gram, and second. For example, the unit of charge is defined as:
statC=cm3/2 g1/2 s−1 in the electrostatic and Gaussian versions, and
abC=cm1/2 g1/2 in the electromagnetic version.
Thus, we see that electric charge has different dimensionality in the electrostatic version than in the electromagnetic version. In both cases, however, the CGS system for mechanics and electromagnetism is 3-dimensional.
With SI there is a base unit for electromagnetism added (ampere for current) to the 3 base units for mechanics. A 4-dimensional system cannot be equivalent to a 3-dimensional system. This is the source of the difficulty in converting units. For mechanics, SI and CGS are both 3-dimensional, and one can say:
1 m = 100 cm, with a true equality so that anywhere the unit symbol m occurs in SI, it can be substituted with 100 cm in all contexts for SI.
However, where one has units in two different dimensions that occurs simply because in one case an independent base unit is involved while the other case is a derived unit, then at best a correspondence occurs—not an equality. The “conversion” factor needed can depend on context. For example:
Both electric charge and electric flux can be measured in coulombs for SI and in statcoulombs for the electrostatic and Gaussian variants of CGS. However,
1 C ≙ 2.998 × 10⁹ statC in the context of electric charge, but
1 C ≙ 3.767 × 10¹⁰ statC in the context of electric flux.
There is a factor 4π between those two correspondences. How are you supposed to know which to use when?
Is that enough to convince you that SI is better than CGS? I was taught in various courses on my way to a PhD in physics that, even though SI matched far better the electromagnetic units we were more used to, from a variety of theoretical considerations CGS is far superior to SI to get a deeper grasp of what is going on in electromagnetism.
Answer:
SI UNITS ARE
MORE RELIABLE
Explanation:
HAVE BEEN USED BY scientists since a long time. It is in accordance with Taditional and Modern Physics.