EC&M's Electrical Calculations Handbook
This is user-friendly, example-rich guide to problem solving strategies in engineering, design, installation, cost estimating, lighting design, and maintenance calculations in electrical work.
TABLE OF CONTENTS EC&M's Electrical Calculations Handbook
Chapter 1: Basic Electrical Working Definitions and Concepts
Electricity is an invisible force that is used to transfer energy into heat, light, intelligence, or motion. Electricity is explained in terms of electrical charge, potential difference (or voltage), electrical charge flow (or current), and resistance to current flow. Figure 1-1 graphically illustrates electron flow through a conductor by comparing it with water flow through a pipe. The normal unit of current measurement is the ampere, whereas the normal unit of voltage measurement is the volt. The unit of opposition to current flow, or resistance, is the ohm.
Figure 1-1: Electric current flow is similar to water flow.
Voltage as Potential Difference
The basic property of every operating electrical system is that different parts of the circuit contain items having different polarities. Another way of saying this is that the "negatively" charged parts contain a surplus of negatively charged electrons, whereas the "positively" charged parts contain a deficiency of electrons. When molecules contain more protons than electrons, they have a deficiency of electrons, and relatively speaking, this means that they have a "positive" overall charge. In nature, there is a natural attraction by protons for sufficient electrons to equalize the positive and negative charges of every molecule. The greater the charge between different parts of the circuit, the greater is the potential difference between them. The standard way of describing this state is to say that the circuit driving voltage, or source voltage, increases.
Surplus electrons exist on the negative ( ?) terminal of a battery, whereas "slots in...
Copyright The McGraw-Hill Companies, Inc. 2001 under license agreement with Books24x7
