Mks system of units

Using the symbol B for the magnetic field technically implies we are using the MKS system of units in which B is given in Tesla (T). Many spectroscopists still express the magnetic field in Gauss (G) — 10 4 T, however, and we will continue that practice here. 

In 1960, the eleventh General Conference on Weights and Measures recommended the International System of Units (Systeme International d Unites), abbreviated as SI units, for use in science SI units are essentially the rationalized mks system of units. Relations between SI units and Gaussian units are given in Table A.4 of the Appendix. Table A.5 allows one to convert equations from SI to Gaussian units. 

In the MKS system of units, standard atmospheric pressure is 750 torr and is expressed as 100,000 Pa (N/m2) or 100 kPa. This means that 1 Pa is equivalent to 7.5 millitorr (1 torr = 133.3 pascal). Vacuum, usually expressed in inches of mercury, is the depression of pressure below the atmospheric level, with absolute zero pressure corresponding to a vacuum of 30 inches of mercuiy. 

In the MKS system of units, s0 is the dielectric constant of vacuum given by... 

We start from Maxwell equations. Using the MKS system of units, we have for wave vector k perpendicular to electric field E the equation [see Eq. (3)]... 

Using the cgs system with the dyne as the unit of force and erg as the unit of work is impractical for many applications (too large or too small numbers to work with), so the mks system of units is preferred. Then the force is in newtons (1 N = 105 dyn), and the unit of work is the joule (1 J = 107 erg). A rate of doing work of 1 J/s is 1 W. A watt is also a measure of electrical power, being 1 A flowing with a potential of 1 V. 

The basic electrostatic units (esu), however, are the unrationalized cgs units. Hence, to convert from unrationalized cgs units to the rationalized mks system of units, start with the relationship... 

In the SI (or MKS) system of units, the joule (J) is a unit of energy, but the electron-volt (eV) is the traditional unit used in ion-solid interactions we can define 1 eV as the kinetic energy gained by an electron accelerated through a potential difference of 1 V. The charge on the electron is 1.602 x 10 19 C, and a joule is a Coulomb-volt, so that the relationship between these units is given by... 

Volt (electric) The unit of potential difference or electromotive force, between two points, in the MKS system of units. In this system 1 coulomb of electric charge will do 1 joule of work in going from one point to the other under 1 volt potential. 

Flux density Power per unit area and per unit frequency of an electromagnetic wave crossing an imaginary plane surface from one side to the other. In observational radio astronomy, the mks system of units is generally used, and the units of flux density are watts per square meter per hertz. 

Prior to the now almost universal adoption of the SI system of units, the unit of heat was defined as the quantity of heat required to raise the temperature of unit mass of water by one degree. This heat quantity is designated the calorie in the cgs system and the kilocalorie in the mks system, and in both cases temperature is expressed in degrees Celsius (Centigrade). As the specific heat capacity is a function of temperature, it has been necessary to set a datum temperature which is chosen as 298 K or 25°C. 

From time to time, probably all science students find themselves entangled in a problem of units. For those who have advanced through physical chemistry to the level of this book, these problems have obviously not been insurmountable. It is likely, however, that —along with feelings of frustration—these students have been left with the wish that everyone used the same units, specifically those units with which they are most comfortable. In response to the recognized need for uniformity, IUPAC recommends the use of Systeme international d unites (International System of Units, SI) units, which are essentially standardized mks units. 

We note, furthermore, that Eq. 5.1 and most of the following relationships are here expressed in the International System of Units (SI), also called the mks system conversion to cgs units is readily accomplished by replacing the factor l/(47i o) by unity. For comparison with measurements, it is customary to use frequencies v in wavenumber units (cm-1). Conversion to these units is accomplished by replacing frequency co (in units of radians/second) by 2ncv, where c designates the speed of light in vacuum furthermore, we replace (5(co) by the identical 3(v)/2nc. 

Note that above we so far employed the absolute (CGS) system of units. Since in most publications deovted to electrolytes SI (MKS) system is usually used, we shall below duplicate the formula for both systems (if these formulas... 

Pressure is defined as force per unit area. In the International System of Units (SI, or mks), unit pressure corresponds to one newton per square meter, which is denoted as one pascal or Pa (named after Blaise Pascal, the seventeenth-century French scientist). There are several other, more commonly used pressure units, however. One is the atmosphere or atm it is... 

Conversion between systems of units often follows this rule-of-thumb 47rsoem in mks versus em in cgs. 

Per unit. In my opinion this expression is a barbarism best avoided. When a student is told that electric field is force per unit Charge and in the MKS system one unit of charge is a coulomb (a huge amount) must we obtain that much charge to measure the field Certainly not. 

All macroscopic aspects of the statics and dynamics of electromagnetic field in the presence of material media are described by Maxwell s equations. The differential form of these axioms in the International System of Units (SI) or rationalized MKS system (Cohen and Giacomo, 1987 Lide, 1991) is given in... 

With the current trend toward metrication, the question of using a consistent system of units has been a problem. Wherever possible, the authors of this Handbook of Environmental Engineering series have used the British system (fps) along with the metric equivalent (mks, cgs, or SIU) or vice versa. For the convenience of the readers around the world, this book provides a 55-page detailed Conversion Factors for Environmental Engineers. In addition, the basic and supplementary units, the derived units and quantities, important physical constants, the properties of water, and the Periodic Table of the Elements, are also presented in this document. 

Another source of confusion might be the units used to report nonlinear optical values. In order to compare the results of two different experiments or confront a theoretical prediction with experimental data, it is necessary to make sure the same units are used. Commonly, in nonlinear optics, CGS (esu) units or MKS units are used. Table 1 lists some fundamental quantities of nonlinear optics, as well as the corresponding units in both CGS (esu) and MKS, together with the conversion factors between the two systems of units [24, 25]. 

Table 1. Fundamental quantities of nonlinear optics and its units in CGS (esu) and MKS. The conversion factor between both systems of units, Q, defined as Necs = 2 I mks where Ncos is the quantity in CGS units, while N ks is the quantity in MKS units, is also provided...

Further, unless otherwise stated, the reader can safely assume we are using the meter-kilo gram-seconds system of units — that is, MKS system, also called the SI system (for System International). 

The measurement of a length or other variable would be impossible without a standard definition of the unit of measurement. For many years science and commerce were hampered by the lack of accurately defined units of measurement. This problem has been largely overcome by precise measurements and international agreements. The internationally accepted system of units of measurements is called the Systeme International d Unites, abbreviated SI. This is an MKS system, which means that length is measured in meters, mass in kilograms, and time in seconds. In 1960 the international chemical community agreed to use SI units. 

It is important to be conversant with the relations, which convert these atomic units of quantum theory into the modem SI [Systeme International] or mks set of units (37) with length measured in metres, m, mass in kilograms, kg, while time is measured in seconds and energy is measured in joules, J, with... 

Together with the SI system, two other unit systems commonly used are the cgs (centimeter-gram-second) and the fps (foot-pound-second). While the cgs system was essentially supplanted by SI units (also termed mks), the fps system is still in use in different parts of the world and most notably in the United States. Conversion between the cgs and SI systems is generally straightforward— usually a factor of 10 or 1000 is involved. Conversion between s (also known as the Imperial system of units) and SI is more complicated. 

MKS system n. A system of units derived from the meter, kilogram, and second. Now superceded for scientific purposes by the SI units, which are based on the MKS system. 

SI n. (1) Abbreviation for silicon or polydi-methylsiloxane. (2) Abbreviation for international systems of units , derived from the official French name, Le System International d Unites. An internationally agreed coherent system of units, derived from the MKS system, now in use for all scientific purposes and thereby replacing the cgs system and the f.p.s. system. The seven basic units are the metric (symbol m), kilogram (kg), second (s), ampere (A), Kelvin (K), mole (mol), and candela (cd). The radian (rad) and steradian (sr) are supplementary units. Derived units include the hertz (Hz), newton (N), joule (J), watt (W), coulomb (C), volt (V), farad (F), ohm (Q), weber (wb), tesla (T), henry (H), lumen (Im), and lux (lx). 

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