Constants and Standards
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DIELECTRIC CONSTANTS OF MATERIALS
The dielectric constants of most materials vary for different ternperatures and frequencies. Likewise, small differences in the composition of materials will cause differences in the dielectric constants. A list of materials and the approximate range (where available) of their dielectric constants are given in Table 2-1. The values shown are accurate enough for most applications. The dielectric constants of sorne materials (such as quarfz, Styrofoam, and Teflon) do not change appreciably with frequency.
| Table 2-1 Dielectric constants of Matrials
| ||||
|---|---|---|---|---|
| Material | Dielectric Constants (Approx.) | Material | Dielectri Constantc (Approx.) | |
| Air Amber Asbestos Fiber Bakelite (asbestos base) Bakelite (mica filled) Barium Titanote Beeswax Cambric (varnished) Carbon Tetrachloride Colluloid Collulose Acetate Durite Ebonite Epoxy Resin Ethyl Alcohol (obsolute) Fiber Formica Glass (electrical) Glass (photogrophic) Glass (Pyrex) Glass (window) Gutta Percha Isolantite Lucite Mico (olectrical) Mica (cloor Indio) Mica (filled phenolic) Micaglass (titanium dioxide) Micarta Mycolex Neoprene | 1.0 2.6-2.7 3.1-4.8 5.0-22 4,5-4.8 100-1250 2.4-2.8 4.0 2.17 4.0 2.9-4.5 4.7-5.1 2.7 3.4-3.7 6.5-25 .0 3.6-6.0 3.8-14.5 7.5 4,6-5.0 7.6 2.4-2.6 6.1 2.5 4.0-9.0 7.5 4.2-5.2 9.0-9.3 3.2-5.5 7.3-9.3 4.0-6.7 | | Nylon Poper (dry) Paper (paraffin coated) Paraffin (solid) Plexiglas Polycorbonate Polyethylene Polyimide Polystyrene Porcelain (dry process) Porcelain (wet process) Quartz Quartz (fused) Rubber (hard) Ruby Mica Selenium (amorphous) Shellac (natural) Silicone (glass) (molding) Silicone (glass) (laminate) Slate Soil (dry) Steatite (ceramic) Steatite (low loss) Styrofoam TefIon Titanium Dioxide Vaseline Vinylite Water (distilled) Waxes, Mineral Wood (dry) | 3.4-22.4 1.5-3.0 2.5-4.0 2.0-3.0 2.6-3.5 2.9-3.2 2.5 3.4-3.5 2.4-3.0 5.0-6.5 5.8-6.5 5.0 3.78 2.0-4.0 5.4 6.0 2.9-3.9 3.2-4.7 3.7-4.3 7.0 2.4-2.9 5.2-6.3 4.4 1.03 2.1 l00 2.16 2.7-7.5 34-78 2.2-2.3 1.4-2.9 |
METRIC SYSTEM
The international system of units developed by the General Conference on Weights and Measures (abbreviated CGPM), commonly called the metric system, is the basis for a worldwide
| Table 2-2. SI Base and Supplementary Units | ||
|---|---|---|
| Quantity | Unit | Symbol |
| length mass time electric current thermodynamic temperature amount of substance luminous intensity plane angle solid angle | meter kilograrn second ampere kelvin * mole candela radiant † steradiont † | m kg s A K mol cd rad sr |
| Table 2-3. SI Derived Units With Special Names | |||
|---|---|---|---|
| Quantity | Unit | Symboll | Formula |
| frequency (of a periodic phenomenon) force pressure, stress energy, work, quantity of heat power, radiant flux quantity of electricity electric charge electric potential, potential difference, electromotive force capacitance electric resistance concluctance magnetic flux magnetic flux density incluctance luminous flux illuminance activity (of radionuclides) obsorbed close | newton pascal joule watt coulomb volt farad ohm siemens weber tesla henry lumen lux becquerel gray | N Pa J W C V F W S Wb T H Im Ix Bq Gy | kg'm/s2 N/m2 N*m J/s A*s W/A C/V V/A AN V*s Wb/m2 Wb/A cd*sr Im/m2 I/s J/kg |
standardization of units. This International System of Units (abbreviated SI) is divided into three classes-base units, supplementary units; and derived units.
Units and Symbols
The seven base units and the two supplementary units with their symbols are given in Table 2-2. Derived units are formed by combining base units, supplementary units and other derived units. Certain derived units have special names and symbols. These units, their symbols and formulas, are given in Table 2-3. Other common derived units,- and their symbols, are given in Table 2-4.
| Table 2-4. Common SI Derived Units | |||
|---|---|---|---|
| Quantity | Unit | Symbol | |
| acceleration angular acceleration angular velocity area concentration (of amount of substance) current density density, mass electric charge density electric field strength electric flux density energy density entropy heat capacity heat flux density irradiance luminance magnetic field strength molar energy molar entropy molar heat capacity moment of force permeability permittivity radiance radiant intensity specific heat capacity specific energy special entropy specific volume surface tension thermal conductivity velocity viscosity, dynamic viscosity, kinernatic volume wovenumber | meter per second squored radian per second squared radion per second square meter mole per cubic meter ampere per square meter kilogram per cubic meter coulomb per cubic meter volt per meter coulomb per square meter joule per cubic meter joule per kelvin joule per kelvin watt per square meter candela per square meter ampere per meter joule per mole joule per mole kelvin joule per mole kelvin newton meter henry per meter farad per meter watt per square meter steradian watt per steradion joule per kilogram kelvin joule per kilogrom joule per kilogram kelvin cubic meter per kilogrom newton per meter watt per meter kelvin meter per second poscal second square meter per second cubic meter l per meter | m/s2 rad/s2 rad/s m2 mol/m3 A/m2 kg/m3 C/m3 V/m C/m2 J/m3 J/K J/K W/M2 cd/m2 A/m J/mol J/(mol*K) J/(mol*K) N-m H/m F/m W/(m2 -sr) W/sr J/(kg*K) J/kg J/(kg*K) M3/kg N/m W/(m*K) m/s Pa*s m2/s m 3 I/m | |
Some units, not part of SI are so widely used they are impractical to abandon. These units Listed in Table 2-5) are acceptable for continued uses.
| Table 2-5 Units in Use With SI | |||
|---|---|---|---|
| Quantity | Unit | Symbol | Value |
| Time Plane angle volume Mass Area (land) | minute hour day week, month, year degree minute second liter metric ton hectare | min h d ° ' " L* t ha | 1 min = 60 s 1 h = 60 min = 3600 s 1 d = 24h = 86,400 s l = (p/I 80) rad 1' = (1/60)° = (p 10800) rad 1" = (1/60)' = (p/648 000) rad 1 L = 11 dml = 10-3 M3 1 t = 103 kg 1 ha = 104 M2 |
Prefixes
The sixteen prefixes in Table 2-6 are used to form multiples and submultiples of the SI units. The use of more than one prefix is to be avoided (e.g. pico instead of micromicro and giga instead of kilomega). The preferred pronunciation of the terms is also included in the table. The accent is on the first syllable of each prefix.
| Table 2-6. Metric Prefixes | |||
|---|---|---|---|
| Muftiplication Factor | Prefix | Abbreviation | Pronunciation |
1015 1012 109 106 103 102 10 10-1 10-2 10-1 10-6 10-9 10-12 10-15 10-16 | peta tera giga mega kilo hecto deka deci centi milli micro nano pico fernto atto | P T G M k h* da* d* C* m ยต n p f a | ex'a (a as in a bout) as in petal as in terrace jig'a (a as in a bout) as in mega phone as in kilowatt heck' toe deck'a (a as in a bout) as in decimal as in sentiment as in military as in microphone nan'oh (an as in ant) peek'oh fern'toe (fem as in feminine) as in anatomy |
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