Fundamental Electrical and Electronic Principles, Third Edition

Chapter 1Fundamentals1.1 UnitsWherever measurements are performed there is a need for a coherentand practical system of units. In science and engineering theInternational System of units (SI units) form the basis of all units used.There are seven ‘ base ’ units from which all the other units are derived,called derived units.Table 1.1 The SI base unitsQuantity Unit Unit symbolMass kilogram kgLength metre mTime second sElectric current ampere ATemperature kelvin KLuminous intensity candela cdAmount of substance mole molA few examples of derived units are shown in Table 1.2 , and it is worthnoting that different symbols are used to represent the quantity and itsassociated unit in each case.Table 1.2 Some SI derived unitsQuantityUnitName Symbol Name SymbolForce F Newton NPower P Watt WEnergy W Joule JResistance R Ohm ΩFor a more comprehensive list of SI units see Appendix A at the backof the book.1