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Voltage in Electrical Systems 1.3.2 Objectives • Define electric potential, or voltage. • Differentiate between AC and DC. • Identify the most common source of DC voltage. • Describe how to connect DC voltage sources so that voltage will be added. • Recall that a field is a model used to help understand and predict how forces are transmitted from one object to another. • Electric field – electric force per unit charge. FE E q Unit is Newton per Coulomb (N/C) Electrical Potential • Potential energy – energy of a particle associated with its position. Gravitational potential difference – ability to accelerate a mass between two heights. GPE = mgh Units: N•m, or J Electric potential difference (or voltage) – ability to accelerate an electric charge between two points in an electric field. V = E d Units: N•m/C, or J/C (or Volt, V) Recall, pressure is a prime mover in fluid sytems. Voltage is a prime mover in electrical systems. The flow of charge is called current. Current continues until the plates are neutral. • Pump is used to maintain pressure difference. • A battery is used to maintain a potential difference. Components of an Electrical System • Load – an appliance or machine. • Conductor – material through which charge can easily flow. • Control element – a switch that turns the current in the system on or off. • Electrical circuit – closed path for current flow created by connecting voltage sources, conductors, control elements, and loads. Direct Current and Alternating Current • Two types of current in electrical systems: • Direct current (DC) – current flows in one direction. • Produced by batteries • Alternating current (AC) – current flows back and forth many time each second. • Produced by alternators • Cell – single unit that houses on or more chemicals. • Electrons and ions are separated in a cell creating a voltage. • Voltage depends on the chemicals used (Table 1.6). • Battery – a collection of two or more cells connected together. • Battery is “dead” when voltage drops below that required to drive the load. • Types of cells (Figure 1.38) • Primary cell – one-time use. • Secondary cell – rechargeable. Connecting Cells to Add Their Voltages • Can be added by connecting cells in series, connecting the positive terminal from one cell to the negative terminal of the next cell. • Individual voltages of each cell adds together (Figure 1.39). • In the circuit, electrons move out of the negative terminal/electrode (or cathode) and enter the positive electrode (or anode) A Simple DC Circuit AC Circuits • Positive and negative terminals change many times per second. • Majority at a rate of 60 cycles per second • Cycling rate, called frequency. • Measured in hertz, cycles per second (1/s, or Hz).