Units, Dimensions, and Standards INTRODUCTION

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5. InductanceThe SI unit of inductance is the 1 henry (H). The inductance of a circuit is 1 henry, whenan emf of 1 volt is induced by the current changing at the rate of 1 A/s.6. CapacitanceThe 2 farad (F) is the SI unit of capacitance.The farad is the capacitance of a capacitor that contains a charge of 1 coulomb when thepotential difference between its terminals is 1 volt.SI TEMPERATURE SCALESThere are two SI temperature scales, the 3 Celsius scale and the 4 Kelvin scale. The Celsiusscale has 100 equal divisions (or degrees) between the freezing temperature and the boilingtemperature of water. At normal atmospheric pressure, water freezes at 0C (zero degreesCelsius) and boils at 100°C.The Kelvin temperature scale, also known as the absolute scale, commences at absolutezero of temperature, which corresponds to 273.15°C. Therefore, 0°C is equal to 273.15 K, and100°C is the same temperature as 373.15 K. A temperature difference of 1 K is the same as atemperature difference of 1°C.OTHER UNIT SYSTEMSIn the traditional English-language (American and Imperial) systems of measurements,the fundamental mechanical units are the foot for length, the pound for mass, and the second fortime. Other mechanical units derived from these are similar in both systems, with the exceptionof the units for liquid measure. The Imperial gallon equals approximately 1.2 U.S. gallons.Before the SI system was adopted, CGS systems using the centimeter, gram, and secondas fundamental mechanical units were employed for scientific purposes. There were two CGSsystems: an electrostatic system and a magnetic system. Many CGS units were too small or toolarge for practical engineering applications, so practical units were also used.When solving problems, it is sometimes necessary to convert from the traditional unitsystems to SI units. Appendix 1 provides a list of conversion factors for this purpose.1. Named for the American physicist Joseph Henry (1797-1878).2. Named for the English chemist and physicist Michael Faraday (1791-1867).3. Invented by the Swedish astronomer and scientist Anders Celsius (1701-1744).4. Named for the Irish-born scientist and mathematician William Thomson, who became Lord Kelvin (1824-1907).6
Example 1-1A bar magnet with a 1 inch square cross section is said to have a total magnetic flux of500 maxwell. Determine the flux density in tesla.SolutionFrom Appendix 1,total flux, = (500 maxwell) × 10 8 Wb= 5µWbarea, A = (1 in.×1 in.) × (2.54×10 2 ) 2 m 2= 2.54 2 ×10 4 m 2flux density, B 5Wb= = A2 4 22.54 10m= 7.75 mTExample 1-2The normal human body temperature is given as 98.6°F. Determine the equivalentCelsius and Kelvin scale temperatures.SolutionFrom Appendix 1,F 32 98.7 32Celsius temperature = =1.8 1.8= 37°CF 32Kelvin temperature = +273.151.8= 310.15 KSTANDARDS1. Working StandardsElectrical measurement standards are precise resistors, capacitors, inductors, voltagesources, and current sources, which can be used for comparison purposes when measuringelectrical quantities. For example, resistance can be accurately measured by means of aWheatstone bridge which uses a standard resistor. Similarly, standard capacitors and inductorscan be employed in bridge (or other) methods to accurately measure capacitance and inductance.The standard resistors, capacitors, and inductors usually found in an electronicslaboratory are classified as working standards. Working standard resistors are normallyconstructed of manganin or a similar material, which has a very low temperature coefficient.They are available in resistance values ranging from 0.01 to 1 M, with typical accuracies of±0.01% to ±0.1%. A working standard capacitor might be air dielectric type, or might beconstructed of silvered mica. Available capacitance values are 0.001 µF to 1 µF with a typicalaccuracy of ±0.02%.Standard inductors are available in values ranging from 100 µH to 10 H with typicalaccuracies of ±0.1%. Calibrators provide standard voltages and currents for calibratingvoltmeters and ammeters.7
Page 2 and 3: 1. Unit of ForceThe SI unit force i
Page 4 and 5: of the metric prefixes in Table 1-1
Page 8 and 9: 2. Standard ClassificationsMeasurem
Page 10: Illumination Unitsfoot-candles lux

Units, Dimensions, and Standards INTRODUCTION

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