Download Voltage in Electrical Systems

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).