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.

q

FE E

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

Electric potential difference (or voltage) – ability to accelerate an electric charge between two points in an electric field.

V = E dUnits: N•m, or J 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).